There are always a lot of questions regarding which RO/DI setup do I need, how many stages, how do I know when to change filters/membranes, I’m getting a weird TDS value, etc. Hopefully this clarifies a few things and helps some of you out one day.
My first recommendation would be to find the best place to put your system, you will need access to a sink or water line depending on if you want to hard plumb the unit or not, and a drain line. Second if you have the space, I would always recommend a traditional setup with either 10” or 20” housings (standard or big blue both work, but the standard 10” is the most common). Proprietary setups/filters are nice and often space saving, but you get stuck with whatever filter designs/options that manufacture makes, they can also be discontinued at any point possibly leaving you to find something else that works or getting a new system entirely.
Now the benefits to a standard housing setup are that you get more flexibility and an easier ability to modify the system to your induvial needs based on your source water. High chlorine or have chloramines? Add a carbon block. High sediment? Add another sediment prefilter. Low source TDS? Add an extra membrane, eliminate your 3 stage DI and run a single mixed bed. You get the idea. Also, eventually most of us will move, so when you move, and your water changes it’s easier to modify the standard housing design to adjust for your new source water. Now you can also add extra standard housings to an existing proprietary system if you already have one, depending on the design of the system you have you may or not be able to add-in between stages of the proprietary design, but you can always add something before or after. So, depending on the problem your trying to solve it may or may not work by adding standard housings before or after.
As a starting point here are some terms from @Buckeye Hydro:
https://www.reef2reef.com/threads/lets-talk-ro-rodi.592882/
A manual on the DOW FilmTec Membranes:
https://www.dupont.com/content/dam/...olutions/public/documents/en/45-D01504-en.pdf
Part 1: Which RO/DI system should I get, and when do I change the filters?
How many stages do I need?
Well this ultimately depends on a variety of factors unique to your location and source water, but by answering a few questions and doing some basic tests you can narrow down what might work best for your situation. First determine if your using well or municipal water. If municipal try to find a recent copy of the water report, what your checking for is chlorine/chloramine. Some reports may not directly state that chloramine is used so you may have to call your supplier to find out. This step is important because if your water contains chloramine it is a good idea to at least be running 2 carbon blocks in order to protect your RO membrane from premature failure. Second what is your source water TDS? If it is high >~300 I’d say it’s a good idea to run at least dual DI resins. This way as one expires you catch it on the second, this isn’t a must, but it will ensure your producing near zero TDS water. Summary: The best system will be built based around your source water parameters. A standard 4 stage will be adequate for most users, but everyone will get a benefit out of a 5+ stage setup, as with most things in this hobby buy the best you can afford. If you can, splurge on the 6 or 7 stage system from the start, even add in a booster pump, dual RO, etc. The nice thing is you could start with a 4 (5,6, or7) stage and add additional housings/components over time to tailor the system to your needs as they change.
What brand of RO/DI unit should I buy?
There are lots of choices in the world for RO/DI units. You will see BRS, SpectraPure, Buckeye Hydro, Aquatic Life, etc. all mentioned on the forum. Well these are all good units you can also find ‘budget’ units on amazon, eBay, etc. So who should you purchase from? Any of the above will work, some better than others, the biggest thing to watch is that on the ‘budget’ units ensure they come with safe (pressure rated) housings. Some of the budget units cannot handle pressures over 80psi without leaking. So just do your homework/research and pick a place that you are comfortable getting your unit from, all of the major manufactures make systems that use the standard 10”x2.5” filters and filters are interchangeable from system to system, that’s the beauty of getting a standard system.
BRS makes several units from 4-7 stages with and without extra features, many hobbyists use these without issue, so its not a bad starting point. SpectraPure also makes high(er) quality units, but you are paying more. Buckeye Hydro also makes quality systems. Aquatic Life also makes solid units as well, so you can’t really go wrong with anyone of these 4 manufactures, some will cost more than others, and to an extent you are getting higher quality pieces/parts so keep that in mind. One note with SpectraPure and Buckeye Hydro they will make custom setups for your needs if you want to reach out to them and have them design a custom setup.
Summary: In alphabetical order: Aquatic Life, BRS, Buckeye Hydro, and SpectraPure all make quality units at different price points.
How many of the bells/whistles do I need on my RO/DI unit?
Well you can run a unit and produce high quality water without any of the fancy bells and whistles it would require more work/monitoring of the system. With that below is what I would consider getting as extras on a system. Some units will come these features, others will not. However, even if your system lacks any of these features they can modified and added in at later dates.
Recommended minimum features for RO/Di setup:
Do I need a booster pump?
Some of us are lucky with higher source water pressure, most of us can get by without the need for a booster pump, but it will improve the system for everyone except those few that already have pressure in the 70+ range. Generally, 80psi is a good point to run and set your booster pump to, but you can theoretically increase it to the rated pressure of the housing or membrane whichever is lower. I would say run in the 80-90psi, but there is room for fluctuation here. The reason for wanting a higher pressure is simple, RO membranes move water by pressure. A simple way to think of it is lower pressure, lower flow/production (more concentrate and less product water), and higher pressure, more flow/production. There is more to it than this, but RO units rely on pressure to produce high quality and high quantities of water. As the pressure increases you will see more product water and less concentrate. If you have a feed supply of >30psi most residential RO units will still produce water, you will just experience longer fill times and higher amounts of concentrate. If your somewhere in the 60psi range, you will be fine but adding a booster down the road will help with your waste/product ratio and filling times.
Summary: While most can get by without one its going to improve the quality and production of water.
What order should I setup my filters?
Sediment –> Carbon Block –> RO Membrane –> DI
Now some of us will run 2 sediment filters, some will run 2 carbon blocks, some with 2 RO membranes, and some with additional DI, regardless of how many of each stage you run for your system they should be that order. If running addental sediment the largest pore size should be first followed by the smaller, same for carbon blocks. So if you have a 1 micron and 5 micron sediment filter, the 5 micron should be first and the 1 micron second, if you have a 1 micron and a 0.5 micron the 1 micron would be first and the 0.5 second, and remember the same applies for carbon blocks. RO membranes if you choose to run more than 1 are typically plumbed in series, so that the waste of the first RO housing feeds the second RO housing. However, if you have a higher incoming TDS you should run your RO membranes in parallel so that they both receive the same source water. Otherwise you will prematurely foul the second RO membrane. The cutoff for high TDS here is debatable, but I would say high would be >~300. Different membranes tolerate TDS differently so some may be fine running in series while others will fail earlier.
Summary: Sediment –> Carbon Block –> RO Membrane –> DI
Why do I need 2 carbon blocks?
You don’t, but it will ensure you remove as much chlorine and chloramine as possible prior to your RO membrane, chorine and chloramine will quickly destroy a RO membrane if left uncontrolled, so running 2 helps to ensure that anything missed by the first gets caught by the second. RO membranes can last 5+ years if you take care of them, the longer it lasts the less you pay to run and operate your system over time.
Summary: You don’t need 2, but don’t you like the idea of a second parachute while skydiving!? It is same–same, but different...
Are running 2 or more stages of DI necessary?
While many run their setups with just a single mixed bed DI resin, it is often recommended to run 2 or more stages of DI. Part of this comes down to source water and part of it as a safety feature. First source water, some water sources will have an unequal balance of compounds that pass through a RO membrane, in this case either the cation or anion media in the DI resin will exhaust prior to the other media. If you’re running a single mixed bed, and your cation is depleting faster than anion resin you will get to a point where the resin is still pulling out anions but not cations. Which will lead to values >0 in your RO/DI water. To eliminate that problem, it is often suggested to either run a second mixed bed DI resin, or separate cation, anion, and a final mixed bed resin. Both options above work, the imbalance between the consumption can be used to determine the most cost-effective solution for you. Another option would be changing the single mixed bed, even if it looks half used (if color changing), in this scenario you are wasting half a DI resin that still has usable life, meaning more $$ to operate your system. If the imbalance is small running a second mixed bed would be a cheaper alternative to throwing away unused resin. In that scenario once the first resin shows any TDS break through the second resin would kick in to remove those compounds. If the second resin shows any breakthrough you would rotate it into the first housing, and by this point you will have gotten as much usable life out of the first as possible and put a new mixed bed in the second housing. The better solution would be to run a 3 or more bed system. So that you are only changing out cation and anion resins as they are depleted, then follow with a mixed bed to ensure anything leftover is caught.
Summary: No, but it will ensure you are constantly producing the highest purity water for your tank and only changing resin when necessary saving you $$.
Should I run more than one RO housing?
This one is optional, it’s not going to help or hurt any of your other filters by running one or two, but it will increase the amount of RO water you can produce in a day. If your trying to increase the speed or the amount of water produced, you will want to run a second membrane. Good news you can add or remove a second membrane as needed. This next part is explained above on another question, but you may have skipped that section, if not this is a repeat. The biggest thing to consider is your source TDS, if you have a high source TDS it is recommended to run your RO membranes in parallel to prevent premature failure of the second RO membrane. If you have a lower TDS you can run your membranes in series, a benefit to running in series less concentrate is produced as the initial concentrate is processed a second time by the second RO membrane, reducing your product to waste ratio.
Summary: It’s not going to hurt anything, and it will increase your daily production if you choose to run two.
How do I know when to change my sediment filer(s)?
Some will simply change them out every couple weeks – couple months. The only harm in changing them early is throwing away usable life costing you more $$ to operate your system. So, what’s the ideal way to change them, pressure gauges. If you have a pressure gauge on the incoming and outgoing side of the filter when you notice a pressure drop of ~10% or more its time to replace your sediment. Often sediment filters will change color or brown out, however, they don’t always lose pressure with the initial color change. So, if your changing your filter every couple weeks because it changes color just realize that filter may still be fine for another 3 or more months depending on pressure drop. Again, changing them earlier is not going to harm your system, so if you don’t mind the extra expense and want to go off color you can certainly continue to do so, but if your aiming for efficiency get yourself some pressure gauges. Another option would be to run a single gauge after your sediment and compare the static pressure with the running pressure.
Summary: Use your incoming vs outgoing pressure readings to change them with the most efficiency. Without gauges, every 3-6 months depending on source water quality and production.
How do I know when to change my carbon filter(s)?
Again, some people will change these out with every sediment filter change or every other sediment change, some will simply do it on a time schedule. While this will work for most, it is dependent on how much water/flow your putting through the filters and your source water chlorine/chloramine values. One of us may be able to just change it every 6 months with no chlorine/chloramine breakthrough, while someone else who changes every 6 months is getting chlorine/chloramine breakthrough because they either produce more water or have higher starting levels of chlorine/chloramine. The best way to know when to change your carbon filters is to pickup a test kit and/or test strips for chlorine/chloramine. Add a sampling port after your last carbon block at a minimum and check the water regularly. If you have multiple carbon blocks a sampling port after each one would be the ideal thing so that you can check each block independently. Different blocks/pore sizes (0.5 micron, 1 micron, 10 micron, etc.) will filter out chlorine/chloramine at different rates, so checking each will ensure you swap them out as needed vs having a useless filter installed while the second block does all the work. The idea here is that the first carbon block removes 90%+ of the chlorine/chloramine, and the second block catches any leftovers, and if you have a 0.5 micron as the second it will help to remove even more compounds before they make it to the membrane. If you have the same filter in both housings, you could also rotate and always keep a fresh carbon block in the second housing to ensure your membrane doesn’t see chlorine/chloramine. When checking chlorine/chloramine levels you want them to be as near 0 as possible, once you see 0.1 or above it’s time to replace to prevent damage to your RO membrane(s). If you don’t have chloramines, no need for a chloramine test kit/strip. Save some cost and stick to chlorine only.
Summary: Get a cheap chlorine and/or chloramine test strip and/or kit and protect your RO membrane.
How do I know when to change my RO membrane(s)?
Some people will replace the RO membrane every year or every other year, while this is fine and will not harm anything to replace them early again you are just spending more $$ than necessary. RO membranes as previously stated function on pressure. That pressure forces pure water through the membrane and into our DI resin. Using the TDS value of the membrane source water and permeate water we can calculate how much TDS is being rejected by the membrane. Most membranes are typically rated >95% rejection. What this means is that 95% of the TDS is removed by the membrane and flushed out as brine, wastewater, or concentrate. For example, if your source TDS is 100, and your membrane is rated at 98%, you should be seeing ~2 TDS in your permeate water. If you’re seeing significantly higher numbers either you have a problem that needs corrected, or your membrane has become fouled and failed. Eventually all membranes will fail and will need to be replaced, but by monitoring your membrane you can replace them at the right time. If you start with a 99% or 98% rejection rated membrane you should be replacing once you start seeing a ~96% rejection rate. The lower the rejection the harder your DI resin will have to work to remove the extra TDS, so while you could a run a membrane down to 90% or even lower you will be burning through more DI to produce high quality water. For that reason, you should be replacing once it loses a few % points of performance. Just monitor your membrane over time and when the performance starts to drop off you know it’s time to start looking for a new one. Keep in mind buying a 98% rated membrane doesn’t mean you will see 98%, your actual % may be higher or lower based on your source water, temperature, and pressure. Most of us will have to replace a membrane every 3-5 years.
Keep in mind that going from a 98% rejection to a 96% rejection will double the amount of resin you burn through. If you start with ~100 TDS water and your permeate water is only 1 TDS, going from 1 to 2 might not seem like a huge increase in resin use since you probably hardly replace them, but that extra 1+ TDS will lead to faster consumption of your resin.
Summary: Monitor your TDS prior and post membrane to ensure you’re not exhausting resin prematurely by sending lower quality water to the DI resin. Buy a high quality membrane such as the DOW FilmTec’s or rebranded DOW FilmTec’s
How can I extend the life of my RO membrane(s)?
The best way to extend the life of your membrane is to ensure minimal chlorine and large sediment makes it to the membrane. Your sediment and carbon pre filters will take care of this for you as long as you maintain those properly. Monitoring for chlorine/chloramine breakthrough is a good place to start. Another important factor when installing new carbon blocks is to remember to flush them for 5+ minutes when installing new ones. You can make it easy and run a ‘T’ fitting and some ball valves to divert water from the last prefilter down to the drain, you can also flush to a bucket if you desire, but running straight to a drain makes it easier. The carbon fines will rapidly clog a RO membrane causing you to have to prematurely replace it. Booster pumps will also help to extend the life of your RO by providing it with more pressure to wash away any build-up and rejected compounds. A good way to do this is by periodically flushing your membrane, the best way would be with a permeate flush kit, but a simple flush with source water will do the job as well. An auto flush is nice since you won’t have to remember to do it, but manual flush valves work the same if you remember. Flushing more frequently will not cause any harm, but not flushing enough will cause build-up and premature failure of the membrane. At a minimum I’d flush at the beginning and end of a production cycle. Ideally every 1-2 hours, but this can vary depending on your source water. If manually flushing you should allow the membrane to flush for at least 30 seconds, but 1-2 minutes would be ideal. New membranes should be flushed for 15+ minutes, and then permeate water discarded for the first 5+ gallons, this will remove any impurities/preservatives from manufacturing/storage.
Summary: Get a booster pump, monitor for chlorine/chloramine breakthrough, flush your pre-filters when replacing, and flush your membrane periodically while running.
Hopefully the above clarifies the different features/setup and answers some questions on when to change filters for a lot of people. Now for part 2.
Part 2: Troubleshooting RO/DI systems.
This is not an all-inclusive list and will hopefully be added to in the future.
I’m not producing any water, help!
One of the tubes are leaking!
My membrane isn’t producing any water!
See the above
My TDS is reading >0 what filters do I change?
So how do I know when to replace my cation bed?
I’m on well water and burning through DI resin!
How do I clean my RO/DI system?
Special thanks to @KStatefan for contributing to, and proofing my post!
My first recommendation would be to find the best place to put your system, you will need access to a sink or water line depending on if you want to hard plumb the unit or not, and a drain line. Second if you have the space, I would always recommend a traditional setup with either 10” or 20” housings (standard or big blue both work, but the standard 10” is the most common). Proprietary setups/filters are nice and often space saving, but you get stuck with whatever filter designs/options that manufacture makes, they can also be discontinued at any point possibly leaving you to find something else that works or getting a new system entirely.
Now the benefits to a standard housing setup are that you get more flexibility and an easier ability to modify the system to your induvial needs based on your source water. High chlorine or have chloramines? Add a carbon block. High sediment? Add another sediment prefilter. Low source TDS? Add an extra membrane, eliminate your 3 stage DI and run a single mixed bed. You get the idea. Also, eventually most of us will move, so when you move, and your water changes it’s easier to modify the standard housing design to adjust for your new source water. Now you can also add extra standard housings to an existing proprietary system if you already have one, depending on the design of the system you have you may or not be able to add-in between stages of the proprietary design, but you can always add something before or after. So, depending on the problem your trying to solve it may or may not work by adding standard housings before or after.
As a starting point here are some terms from @Buckeye Hydro:
https://www.reef2reef.com/threads/lets-talk-ro-rodi.592882/
A manual on the DOW FilmTec Membranes:
https://www.dupont.com/content/dam/...olutions/public/documents/en/45-D01504-en.pdf
Part 1: Which RO/DI system should I get, and when do I change the filters?
How many stages do I need?
Well this ultimately depends on a variety of factors unique to your location and source water, but by answering a few questions and doing some basic tests you can narrow down what might work best for your situation. First determine if your using well or municipal water. If municipal try to find a recent copy of the water report, what your checking for is chlorine/chloramine. Some reports may not directly state that chloramine is used so you may have to call your supplier to find out. This step is important because if your water contains chloramine it is a good idea to at least be running 2 carbon blocks in order to protect your RO membrane from premature failure. Second what is your source water TDS? If it is high >~300 I’d say it’s a good idea to run at least dual DI resins. This way as one expires you catch it on the second, this isn’t a must, but it will ensure your producing near zero TDS water. Summary: The best system will be built based around your source water parameters. A standard 4 stage will be adequate for most users, but everyone will get a benefit out of a 5+ stage setup, as with most things in this hobby buy the best you can afford. If you can, splurge on the 6 or 7 stage system from the start, even add in a booster pump, dual RO, etc. The nice thing is you could start with a 4 (5,6, or7) stage and add additional housings/components over time to tailor the system to your needs as they change.
What brand of RO/DI unit should I buy?
There are lots of choices in the world for RO/DI units. You will see BRS, SpectraPure, Buckeye Hydro, Aquatic Life, etc. all mentioned on the forum. Well these are all good units you can also find ‘budget’ units on amazon, eBay, etc. So who should you purchase from? Any of the above will work, some better than others, the biggest thing to watch is that on the ‘budget’ units ensure they come with safe (pressure rated) housings. Some of the budget units cannot handle pressures over 80psi without leaking. So just do your homework/research and pick a place that you are comfortable getting your unit from, all of the major manufactures make systems that use the standard 10”x2.5” filters and filters are interchangeable from system to system, that’s the beauty of getting a standard system.
BRS makes several units from 4-7 stages with and without extra features, many hobbyists use these without issue, so its not a bad starting point. SpectraPure also makes high(er) quality units, but you are paying more. Buckeye Hydro also makes quality systems. Aquatic Life also makes solid units as well, so you can’t really go wrong with anyone of these 4 manufactures, some will cost more than others, and to an extent you are getting higher quality pieces/parts so keep that in mind. One note with SpectraPure and Buckeye Hydro they will make custom setups for your needs if you want to reach out to them and have them design a custom setup.
Summary: In alphabetical order: Aquatic Life, BRS, Buckeye Hydro, and SpectraPure all make quality units at different price points.
How many of the bells/whistles do I need on my RO/DI unit?
Well you can run a unit and produce high quality water without any of the fancy bells and whistles it would require more work/monitoring of the system. With that below is what I would consider getting as extras on a system. Some units will come these features, others will not. However, even if your system lacks any of these features they can modified and added in at later dates.
Recommended minimum features for RO/Di setup:
- Pressure gauge for RO feed water
- TDS meter for RO feed water
- TDS meter for RO product water (permeate water)
- TDS meter for final RO/DI water (after DI resin(s))
- Pressure gauge for incoming source water (pre sediment/carbon)
- Pressure gauge for RO feed water (post sediment/carbon)
- TDS meter for RO feed water (post sediment/carbon)
- TDS meter for RO product water (permeate water)
- TDS meter for each stage of DI (out of each canister)
- For example, if your running dual stages 1 meter for the out of the first canister, and 1 meter for the out of the second canister.
- Automatic Flush valve
- Bypass/flush/drain valves for filtered water, RO water, concentrate water
- Same as above, except remove the automatic flush and replace it with
- Automatic permeate flush kit
- This will flush the membrane with your RO/DI water (0 TDS) which will eliminate TDS creep and extend the life of the membrane by removing more of the contaminates.
Do I need a booster pump?
Some of us are lucky with higher source water pressure, most of us can get by without the need for a booster pump, but it will improve the system for everyone except those few that already have pressure in the 70+ range. Generally, 80psi is a good point to run and set your booster pump to, but you can theoretically increase it to the rated pressure of the housing or membrane whichever is lower. I would say run in the 80-90psi, but there is room for fluctuation here. The reason for wanting a higher pressure is simple, RO membranes move water by pressure. A simple way to think of it is lower pressure, lower flow/production (more concentrate and less product water), and higher pressure, more flow/production. There is more to it than this, but RO units rely on pressure to produce high quality and high quantities of water. As the pressure increases you will see more product water and less concentrate. If you have a feed supply of >30psi most residential RO units will still produce water, you will just experience longer fill times and higher amounts of concentrate. If your somewhere in the 60psi range, you will be fine but adding a booster down the road will help with your waste/product ratio and filling times.
Summary: While most can get by without one its going to improve the quality and production of water.
What order should I setup my filters?
Sediment –> Carbon Block –> RO Membrane –> DI
Now some of us will run 2 sediment filters, some will run 2 carbon blocks, some with 2 RO membranes, and some with additional DI, regardless of how many of each stage you run for your system they should be that order. If running addental sediment the largest pore size should be first followed by the smaller, same for carbon blocks. So if you have a 1 micron and 5 micron sediment filter, the 5 micron should be first and the 1 micron second, if you have a 1 micron and a 0.5 micron the 1 micron would be first and the 0.5 second, and remember the same applies for carbon blocks. RO membranes if you choose to run more than 1 are typically plumbed in series, so that the waste of the first RO housing feeds the second RO housing. However, if you have a higher incoming TDS you should run your RO membranes in parallel so that they both receive the same source water. Otherwise you will prematurely foul the second RO membrane. The cutoff for high TDS here is debatable, but I would say high would be >~300. Different membranes tolerate TDS differently so some may be fine running in series while others will fail earlier.
Summary: Sediment –> Carbon Block –> RO Membrane –> DI
Why do I need 2 carbon blocks?
You don’t, but it will ensure you remove as much chlorine and chloramine as possible prior to your RO membrane, chorine and chloramine will quickly destroy a RO membrane if left uncontrolled, so running 2 helps to ensure that anything missed by the first gets caught by the second. RO membranes can last 5+ years if you take care of them, the longer it lasts the less you pay to run and operate your system over time.
Summary: You don’t need 2, but don’t you like the idea of a second parachute while skydiving!? It is same–same, but different...
Are running 2 or more stages of DI necessary?
While many run their setups with just a single mixed bed DI resin, it is often recommended to run 2 or more stages of DI. Part of this comes down to source water and part of it as a safety feature. First source water, some water sources will have an unequal balance of compounds that pass through a RO membrane, in this case either the cation or anion media in the DI resin will exhaust prior to the other media. If you’re running a single mixed bed, and your cation is depleting faster than anion resin you will get to a point where the resin is still pulling out anions but not cations. Which will lead to values >0 in your RO/DI water. To eliminate that problem, it is often suggested to either run a second mixed bed DI resin, or separate cation, anion, and a final mixed bed resin. Both options above work, the imbalance between the consumption can be used to determine the most cost-effective solution for you. Another option would be changing the single mixed bed, even if it looks half used (if color changing), in this scenario you are wasting half a DI resin that still has usable life, meaning more $$ to operate your system. If the imbalance is small running a second mixed bed would be a cheaper alternative to throwing away unused resin. In that scenario once the first resin shows any TDS break through the second resin would kick in to remove those compounds. If the second resin shows any breakthrough you would rotate it into the first housing, and by this point you will have gotten as much usable life out of the first as possible and put a new mixed bed in the second housing. The better solution would be to run a 3 or more bed system. So that you are only changing out cation and anion resins as they are depleted, then follow with a mixed bed to ensure anything leftover is caught.
Summary: No, but it will ensure you are constantly producing the highest purity water for your tank and only changing resin when necessary saving you $$.
Should I run more than one RO housing?
This one is optional, it’s not going to help or hurt any of your other filters by running one or two, but it will increase the amount of RO water you can produce in a day. If your trying to increase the speed or the amount of water produced, you will want to run a second membrane. Good news you can add or remove a second membrane as needed. This next part is explained above on another question, but you may have skipped that section, if not this is a repeat. The biggest thing to consider is your source TDS, if you have a high source TDS it is recommended to run your RO membranes in parallel to prevent premature failure of the second RO membrane. If you have a lower TDS you can run your membranes in series, a benefit to running in series less concentrate is produced as the initial concentrate is processed a second time by the second RO membrane, reducing your product to waste ratio.
Summary: It’s not going to hurt anything, and it will increase your daily production if you choose to run two.
How do I know when to change my sediment filer(s)?
Some will simply change them out every couple weeks – couple months. The only harm in changing them early is throwing away usable life costing you more $$ to operate your system. So, what’s the ideal way to change them, pressure gauges. If you have a pressure gauge on the incoming and outgoing side of the filter when you notice a pressure drop of ~10% or more its time to replace your sediment. Often sediment filters will change color or brown out, however, they don’t always lose pressure with the initial color change. So, if your changing your filter every couple weeks because it changes color just realize that filter may still be fine for another 3 or more months depending on pressure drop. Again, changing them earlier is not going to harm your system, so if you don’t mind the extra expense and want to go off color you can certainly continue to do so, but if your aiming for efficiency get yourself some pressure gauges. Another option would be to run a single gauge after your sediment and compare the static pressure with the running pressure.
Summary: Use your incoming vs outgoing pressure readings to change them with the most efficiency. Without gauges, every 3-6 months depending on source water quality and production.
How do I know when to change my carbon filter(s)?
Again, some people will change these out with every sediment filter change or every other sediment change, some will simply do it on a time schedule. While this will work for most, it is dependent on how much water/flow your putting through the filters and your source water chlorine/chloramine values. One of us may be able to just change it every 6 months with no chlorine/chloramine breakthrough, while someone else who changes every 6 months is getting chlorine/chloramine breakthrough because they either produce more water or have higher starting levels of chlorine/chloramine. The best way to know when to change your carbon filters is to pickup a test kit and/or test strips for chlorine/chloramine. Add a sampling port after your last carbon block at a minimum and check the water regularly. If you have multiple carbon blocks a sampling port after each one would be the ideal thing so that you can check each block independently. Different blocks/pore sizes (0.5 micron, 1 micron, 10 micron, etc.) will filter out chlorine/chloramine at different rates, so checking each will ensure you swap them out as needed vs having a useless filter installed while the second block does all the work. The idea here is that the first carbon block removes 90%+ of the chlorine/chloramine, and the second block catches any leftovers, and if you have a 0.5 micron as the second it will help to remove even more compounds before they make it to the membrane. If you have the same filter in both housings, you could also rotate and always keep a fresh carbon block in the second housing to ensure your membrane doesn’t see chlorine/chloramine. When checking chlorine/chloramine levels you want them to be as near 0 as possible, once you see 0.1 or above it’s time to replace to prevent damage to your RO membrane(s). If you don’t have chloramines, no need for a chloramine test kit/strip. Save some cost and stick to chlorine only.
Summary: Get a cheap chlorine and/or chloramine test strip and/or kit and protect your RO membrane.
How do I know when to change my RO membrane(s)?
Some people will replace the RO membrane every year or every other year, while this is fine and will not harm anything to replace them early again you are just spending more $$ than necessary. RO membranes as previously stated function on pressure. That pressure forces pure water through the membrane and into our DI resin. Using the TDS value of the membrane source water and permeate water we can calculate how much TDS is being rejected by the membrane. Most membranes are typically rated >95% rejection. What this means is that 95% of the TDS is removed by the membrane and flushed out as brine, wastewater, or concentrate. For example, if your source TDS is 100, and your membrane is rated at 98%, you should be seeing ~2 TDS in your permeate water. If you’re seeing significantly higher numbers either you have a problem that needs corrected, or your membrane has become fouled and failed. Eventually all membranes will fail and will need to be replaced, but by monitoring your membrane you can replace them at the right time. If you start with a 99% or 98% rejection rated membrane you should be replacing once you start seeing a ~96% rejection rate. The lower the rejection the harder your DI resin will have to work to remove the extra TDS, so while you could a run a membrane down to 90% or even lower you will be burning through more DI to produce high quality water. For that reason, you should be replacing once it loses a few % points of performance. Just monitor your membrane over time and when the performance starts to drop off you know it’s time to start looking for a new one. Keep in mind buying a 98% rated membrane doesn’t mean you will see 98%, your actual % may be higher or lower based on your source water, temperature, and pressure. Most of us will have to replace a membrane every 3-5 years.
Keep in mind that going from a 98% rejection to a 96% rejection will double the amount of resin you burn through. If you start with ~100 TDS water and your permeate water is only 1 TDS, going from 1 to 2 might not seem like a huge increase in resin use since you probably hardly replace them, but that extra 1+ TDS will lead to faster consumption of your resin.
Summary: Monitor your TDS prior and post membrane to ensure you’re not exhausting resin prematurely by sending lower quality water to the DI resin. Buy a high quality membrane such as the DOW FilmTec’s or rebranded DOW FilmTec’s
How can I extend the life of my RO membrane(s)?
The best way to extend the life of your membrane is to ensure minimal chlorine and large sediment makes it to the membrane. Your sediment and carbon pre filters will take care of this for you as long as you maintain those properly. Monitoring for chlorine/chloramine breakthrough is a good place to start. Another important factor when installing new carbon blocks is to remember to flush them for 5+ minutes when installing new ones. You can make it easy and run a ‘T’ fitting and some ball valves to divert water from the last prefilter down to the drain, you can also flush to a bucket if you desire, but running straight to a drain makes it easier. The carbon fines will rapidly clog a RO membrane causing you to have to prematurely replace it. Booster pumps will also help to extend the life of your RO by providing it with more pressure to wash away any build-up and rejected compounds. A good way to do this is by periodically flushing your membrane, the best way would be with a permeate flush kit, but a simple flush with source water will do the job as well. An auto flush is nice since you won’t have to remember to do it, but manual flush valves work the same if you remember. Flushing more frequently will not cause any harm, but not flushing enough will cause build-up and premature failure of the membrane. At a minimum I’d flush at the beginning and end of a production cycle. Ideally every 1-2 hours, but this can vary depending on your source water. If manually flushing you should allow the membrane to flush for at least 30 seconds, but 1-2 minutes would be ideal. New membranes should be flushed for 15+ minutes, and then permeate water discarded for the first 5+ gallons, this will remove any impurities/preservatives from manufacturing/storage.
Summary: Get a booster pump, monitor for chlorine/chloramine breakthrough, flush your pre-filters when replacing, and flush your membrane periodically while running.
Hopefully the above clarifies the different features/setup and answers some questions on when to change filters for a lot of people. Now for part 2.
Part 2: Troubleshooting RO/DI systems.
This is not an all-inclusive list and will hopefully be added to in the future.
I’m not producing any water, help!
- Ensure your water line is turned on, whether it’s a sink connection or a ball valve!
- Have you plumbed the system correctly? (If new install, or recent modifications)
- If you have pressure gauges installed what are the readings?
- Check source water supply, and then remainder of unit for clog, shut water supply off prior to dissembling any equipment.
- Is it time to change any of your prefilters?
- Check your auto shut-off valve
One of the tubes are leaking!
- Tubing may not be properly inserted fully or may have been cut at an improper angle. Tubing should be cut straight in order to form a proper seal.
- Tubing can develop pinhole leaks over time, for this reason it’s recommended to keep a supply of spare tubing on hand just in case.
My membrane isn’t producing any water!
- If newly installed, ensure you have it seated properly into the housing(s). You should hear a ‘pop’ or ‘click’ when they are fully seated into the housing. If not, they may not be fully installed.
- Is it installed correctly, supply, waste, permeate lines?
- Check the seal around the membrane (rubber O-ring) for any tears/holes.
- Did you flush your carbon filters prior to sending that water to the membrane?
- How old is your membrane and what was the last known rejection %?
- How old is your membrane housing? Wrapped, cracked, scratched housings can lead to bypass of the membrane
See the above
My TDS is reading >0 what filters do I change?
- If you only have a single DI resin, it’s time to replace.
- If you are seeing >0 TDS out of the first DI cartridge, and you have a second installed, it is time to put a new resin in the second housing and rotate the current resin from the second to the first housing.
- If you are using a 3 bed system with cation, anion, and mixed bed, it will depend on where the TDS is reading >0. A reading >0 from the cation bed is nothing to worry about, a >0 from the anion or mixed bed means something needs replaced. If anion >0 replace anion bed if cation doesn’t need replaced. If final mixed bed >0 then anion and mixed beds both need replaced, and possibly cation as well.
- Use color changing resin
So how do I know when to replace my cation bed?
- For a 3 bed setup you should monitor TDS after each housing and prior to the first (typically this is done for the incoming as a permeate line off the RO membrane). If your permeate is reading 10 TDS, and your cation is reading 10 TDS it’s time to replace. You should note your initial reading for TDS from the cation resin with each new install. If your permeate water is 10 TDS and your cation reads 5 TDS upon initial install, then if your permeate water is reading 10 TDS and your cation reads >5 it would be time to replace. If your permeate TDS goes up, the reading for the cation TDS would increase as well most likely. Color changing resin which many people use removes some of the monitoring in this process.
- Use color changing resin
I’m on well water and burning through DI resin!
- Strong possibility you have high levels of CO2 in your water.
- Let the permeate water off gas prior to running through DI
- Setup a 3 bed system
- DIY CO2 Degassing Chamber for RO/DI:
- https://www.reef2reef.com/threads/diy-co2-degassing-chamber-for-ro-di.212587/
- RO/DI systems should be cleaned once per year.
- Many of you may have not ever cleaned your system and have never had an issue
- The quality of your water will ultimately determine how frequently you should be cleaning your system. Some may require more or less frequent cleaning to prevent any fouling/contamination.
- If you have a bladder tank and use your RO system for drinking water you should be cleaning the system at least once per year, if you are using it strictly for your tank it is still a good idea to clean the system, but more than likely you will be fine cleaning less frequently.
How do I clean my RO/DI system?
- There are commercially available options from several different manufactures/sites.
- Another way to flush the system with regular bleach.
- Remove all filters from the system, fill the first housing up with ~1/2 cup bleach, reinstall all housings (without any filters) fill the system up with water and flush until the bleach solution goes through the entire system. Once the system has been filled with the bleach solution, let it sit for at least 30 minutes, remove all the housings and dispose of the water. Reinstall the housings (without filters) and flush the system with water for ~15 minutes. Remove the housings and reinstall filters. Flush the system as normal when replacing filters and being normal operation.
- Make sure not to use bleach on your RO membrane. If you want to sanitize the membrane you can use a commercially available cleaner for the system, or a 0.1% hydrogen peroxide solution (prepared with RO/DI water)
Special thanks to @KStatefan for contributing to, and proofing my post!
