Ro/di system

[Stinger]

I guess I'm learning. I purchased a used RO/DI Maxima unit, with 35gpd membrane. The guy told me he changed membrane out 3 months earlier. Also all filters 5 months before that. So i hooked it up and ran my ro/di water , been adding to my 110 for 6 weeks now, my tank has been running for 9 weeks now. All params look good. could not figure out why i'm still getting some diatoms in my 110 tank. It still has some silicone's in the water. I hooked up my TDS meter today and got 122 in and 16 to 17 out!! gotta order new carbon and Di filter./ I changed sentiment filter 2 weeks ago . Im getting there !! tank just completed 9 weeks.So advice from a beginner like me. When buying used RO/DI units , change all filters first. DUHHH:cry:

 

[JohnSalt]

with a rodi system its also important to know the rejection rate of the ro membrane. That way you can do some testing, and a few calculations to make sure the most important part (the ro membrane) is functioning properly, and not over-working expensive di resin.

example.... tds of water going in 300
tds of water coming out of the ro membrane (before the di) is 4 - 8ish.
If the rejection rating of the membrane used here is %98 , then its working perfect, and the di resin will polish off the rest of the tds.
the pre filter and carbon filter shouldn't have any effect at all on the tds of the output water, only slow flow from clogging, or...... an exhausted carbon filter can allow chlorine to pass through and damage the ro membrane. If that happens thats when the tds of the "ro out" water will exceed the rejection rate calculation.

 

[Stinger]

Thanks for the info John

 

[bigorange]

I have a six stage RoDi that I just changed everything but the RoDi membrane. I am getting 4tds is that okay? I was thinking since everything was changed it would be 0-2

Sent from my EVO3d using tapatalk

 

[Stinger]

OK, so after I removed my sensor and cleaned with alcohol, then let air dry. I am getting 4TDS. which i hear is not bad. But 0TDS is what we want. according to internet reading when you get 6 or 7 you need to change all filters.

 

[AZDesertRat]

To troubleshoot a RO/DI system you need three TDS measurements, tap water TDS, RO only TDS before the DI and final or RO/DI TDS. Without all three you have no idea how well the membrane is performing.
A new RO membrane should be 96-98% efficient or rejection rate. To calculate the rejection rate you need the tap water TDS and the RO only TDS. The formula is tap TDS-RO TDS/tap TDSx100.
As an example say your tap TDS is about the national average of 250 and your RO only TDS is 10. So, 250-10=240, 240/250=.96, .96x100= 96% rejection rate or removal efficiency.

96% is about the bottom of where you want to be. The reason is for every 2% your rejection rate drops, your DI resin life is cut in half. Yes, every 2% drop in efficieny cuts your DI life in half so the inverse is for every 2% you can increase the membranes efficiency you double the life of your DI. It does not take more than a few DI replacements to pay for a new more efficient RO membrane so it could be a wise purchase.

For the RO/DI your goal is 0 TDS, noting else is acceptable since you have no idea what that TDS is made up of. This is important since DI resins start to release weakly ionized substances even before it is exhausted and some of those weakly ionized substances are nitrates (actually all forms of ammonia), silicates and phosphates, none of which you want. RO membranes by themselves are not particularly effective at any of those three so you need high quality DI resin and a good membrane to remove them all to reef quality levels.

Sediment filters and csrbon blocks have very little to absolutely noting to do with TDS, their sole purpose is to protect the RO membrane from sediment, silt, particulates, colloidal materials and of course chlorine. Suspended solids in other words, TSS not TDS or Total Dissolved Solids. TSS or suspended solids can be anywhere from visible to the naked eye (you can visibly see particles down to about 40 microns with the unaided eye) down to around 0.1 microns depending on the quality of your sediment and carbon filters. TDS on the other hand is not visible, are in the 0.0001 micron range, can be measured with a TDS or conductivity meter, and are the job of the membrane and DI to remove. Using a TDS reading as a gauge of filter condition does no twork.

You change the sediment andcarbon filters every 6 months like clockwork and disinfect the system with nromal household bleach according to the vendors directions to protect the RO membrane. You replace the DI resin when you first start to see anything other than 0 TDS in the finsihed water on a consistent basis. You replace the RO membrane when it is no longer cost effective to keep replacing the DI resin, usually in the 95-96% rejection rate range.

The membrane and the DI are the only things taht effect TDS so it is important to protect them with high quality, low micron replacement filters and carbons every 6 months so they can do their job.

 

[iprayforwaves]

Its a pain sometimes keeping track of the sediment filters and when its time to change them, but its worth it to protect your investment in the RO membrane. I use the color-changing DI resin from BRS, turns brown when exhausted. Nice visual cue.

 

[AZDesertRat]

Keeping track of the sediment and carbon block changes is easy, take a Sharpie and put the date right on the bracket or housing so it stands out and you see it every 6 months.
Color changing DI resins are for the most part a waste of money. Resins change in streaks, not at all, top to bottom, bottom to top and almost always too late. If you use your TDS meter you will find you are passing significant TDS before the resins change color and could be doing harm since its the weakly ionized substances that are being released first. Just get in the habit of using your TDS meter and you will be better off.

 

[Stinger]

Keeping track of the sediment and carbon block changes is easy, take a Sharpie and put the date right on the bracket or housing so it stands out and you see it every 6 months.
Color changing DI resins are for the most part a waste of money. Resins change in streaks, not at all, top to bottom, bottom to top and almost always too late. If you use your TDS meter you will find you are passing significant TDS before the resins change color and could be doing harm since its the weakly ionized substances that are being released first. Just get in the habit of using your TDS meter and you will be better off.

+1 , now this makes sense!! my di only changed colors a lil, but the TDS meter says otherwise. I think i will trust my TDS meter from here on. Thanks AZDesertrat

 

[AZDesertRat]

If you are using bulk DI resin make sure you are packing the cartridge correctly. Start by filling the cartridge to the top then tap it on the table of counter top several times so it packs down. Add more resin, tap it on the table a few more times, add more and tap again if needed. Place the spone donut back on top of the resin and screw the lid on snug.

Most people don't realize, resin shrinks slightly with use so you end up with spaces or voids in the resin bed which cause the resins to seperate or stratify since anion and cation resins have different weights so one may sink to the bottom. If its packed tightly it will stay mixed and usually works better and longer.

 

[Ashlar]

An inline TDS meter is a wonderful investment.

 

[AZDesertRat]

They are a good guide but not as accurate nor as versatile as a good handheld TDS meter. The inlines are dedicated to one or two points and cannot be used portable since they require flow past the probes to operate. They are also not temperature compensated, they actually sense room air temperature and not wate rtemperature which are rarely the same so can be significantly off. A handheld has a temperature probe built in so it automatically temperature compensated and can be very accurate if kept clean and calibrated. Thye can also be used about anywhere including tap water, LFS water, RO only water, RO/DI water, your ATO reservoir, bottled water, your buddies house and tank etc.
The cost of both is minimal at about $25 so its actually a good idea to have both, I have two of each myself and use the inlines as a rough indicator or litmus paper type test and the COM-100 handheld for accuracy and when to change DI resins.