Salinity Drops Every Time ATO Adds RODI — Normal or Something Wrong?

[Alexr54]

I’m looking for some input on salinity swings I’m seeing in my tank.

The graph from my Apex shows each time my tank auto tops off with RODI water compared against the salinity reading. I know the Apex salinity probe is not calibrated perfectly, and I don’t really rely on it for my actual salinity number. I mostly use it to watch for spikes, drops, and general trends.

For my actual salinity testing, I use a calibrated digital Milwaukee tester.

That said, my Milwaukee tester also shows a similar drop in salinity after the ATO runs, so it does not appear to be only an Apex probe issue.

This is on a fairly new 69 gallon Red Sea Reefer tank (8 months). I also have an older 175 gallon aquarium that has been running for15+ years, and I almost never need to add salt to that system. It also has an Apex with a salinity probe and i do not see these spikes when the ATO runs.

With this newer tank, I feel like I have had to add salt at a much higher rate than I am used to. I understand this tank has a much lower total water volume than my older setup, so maybe the swings are just more noticeable, but I’m not sure if this is normal or if something else is going on.

I have checked the system for leaks, drips, salt creep, and anything else obvious, but I have not found anything that would correlate with the graph data. I also have leak detectors placed around the tank, and none of them have ever gone off.

What do you all think could be causing these salinity drops every time the ATO fills? Is this normal behavior in a smaller system, or should I be looking for something specific?

 

[exnisstech]

I would expect a drop when fresh water is added. I don't monitor tho only test so I don't know what would be considered normal. I never understood the need to monitor salinity TBO because mine has never fluctuated enough between testing that I have to make adjustments. I think sometimes we tend to want to see too much going on just because we can not because we need to. But that's JMO and I've never used a controller. I'm sure someone running a controller can contribute something useful

 

[Alexr54]

I would expect a drop when fresh water is added. I don't monitor tho only test so I don't know what would be considered normal. I never understood the need to monitor salinity TBO because mine has never fluctuated enough between testing that I have to make adjustments. I think sometimes we tend to want to see too much going on just because we can not because we need to. But that's JMO and I've never used a controller. I'm sure someone running a controller can contribute something useful

I was doing a bit more thinking on this.
I have a DOS that I use for15g trickle water changes over a month duration.
I’m thinking the calibration of the DOS may be messed up where it dumps more than it adds.
I’m going to redo that calibration just to be sure

I like to automate EVERYTHING. It’s an obsession.

 

[Alexr54]

I would expect a drop when fresh water is added. I don't monitor tho only test so I don't know what would be considered normal. I never understood the need to monitor salinity TBO because mine has never fluctuated enough between testing that I have to make adjustments. I think sometimes we tend to want to see too much going on just because we can not because we need to. But that's JMO and I've never used a controller. I'm sure someone running a controller can contribute something useful

My scenario is a perfect example of why monitoring it is useful. :-D
Unless I used my Milwaukee salinity tester all the time (which I don’t) I would have never known something looks wrong here.

 

[exnisstech]

Ya I'm a simpleton and my only automation is ATO units and one tank with a doser. I manually dose 3 other tanks lol. I'm also never away from home more than a few hours at a time which isn't a luxury everyone has.

 

[exnisstech]

My scenario is a perfect example of why monitoring it is useful. :-D
Unless I used my Milwaukee salinity tester all the time (which I don’t) I would have never known something looks wrong here.

Understood but what is the cause of the fluctuations I have 4 tanks running that don't fluctuate.

 

[Alexr54]

Understood but what is the cause of the fluctuations I have 4 tanks running that don't fluctuate.

Currently I’m thinking it’s my DOS calibration being off that performs a 15g water change over 30 days. Its dumping more then it’s adding.
Thats all I can think of so far.

It’s gradually dumping salt water while gradually adding a lesser amount of salt water. Then when it reaches the low point where my ATO starts to fill it with RODI it’s just adding more freshwater and causing the salt to do these drops each time.

 

[Vivid Creative Aquatics Verified Sponsor]

That is a pretty significant drop - even on a 69-gallon tank.

How is the ATO determining when to add water? is it a float sensor, optical sense or the level sensor?

 

[exnisstech]

Automation is the cause you think lol
Just picking . We all run things the way we enjoy or need to do depending in circumstances.
I've been tempted to look onto an AWC because I have to pump water from the basement to the first floor. I'm sure if I had only one tank I would be testing the waters with some automation but with 4 it's just too much. I also spent too many years repairing replacing faiied components, many electronics so I see almost everything as a point of failure, it's just a matter if when not if.

 

[Alexr54]

That is a pretty significant drop - even on a 69-gallon tank.

How is the ATO determining when to add water? is it a float sensor, optical sense or the level sensor?

Thanks! At least I know I’m not overreacting now. It is a lot huh.

Water level sensor. I find it more easy to use and more accurate than the optical ATO sensors.
I have the ATK in my other tank with the optical sensors. And they can get dirty and start giving false readings. And another magnet to add to my refugium/sump. :)

I even got another ATK for this new tank but decided not to use it (still in the box).
Also with the level sensor I find it’s better when it comes to chattering (repeated start/stop).
I’ve had to add a bunch more code on the ATK setup to prevent that.

 

[Alexr54]

Automation is the cause you think lol
Just picking . We all run things the way we enjoy or need to do depending in circumstances.
I've been tempted to look onto an AWC because I have to pump water from the basement to the first floor. I'm sure if I had only one tank I would be testing the waters with some automation but with 4 it's just too much. I also spent too many years repairing faiied component, many electronics so I see almost everything as a point of failure, it's just a matter if when not if.

I have 2 both with a bunch of Neptune equipment. Things add up fast.

 

[Alexr54]

I also have a trident ACM and trident NP on this tank.
I was thinking maybe its from the test sample water being dumped.
But thinking more about that - it takes like 6 months to fill up 2 gallons with sample water AND reagent (1g for each trident). This drop of salinity is too fast to attribute to the water tests.

 

[rtparty]

For salinity to continuously drop like that means you are removing more saltwater than is being added back to the tank. This can happen with AWC and skimmers. AWC removes saltwater and should replace it with saltwater but if your amounts aren’t the same, you will see salinity trend one way.

With a skimmer, it removes SW but that is replaced by RO water usually. Thus, salinity will slowly fall

 

[Alexr54]

For salinity to continuously drop like that means you are removing more saltwater than is being added back to the tank. This can happen with AWC and skimmers. AWC removes saltwater and should replace it with saltwater but if your amounts aren’t the same, you will see salinity trend one way.

With a skimmer, it removes SW but that is replaced by RO water usually. Thus, salinity will slowly fall

Thanks. Yes i made sure i am not wet skimming.
Im also leaning towards the AWC calibrations.

 

[Vivid Creative Aquatics Verified Sponsor]

Thanks! At least I know I’m not overreacting now. It is a lot huh.

Water level sensor. I find it more easy to use and more accurate than the optical ATO sensors.
I have the ATK in my other tank with the optical sensors. And they can get dirty and start giving false readings. And another magnet to add to my refugium/sump. :)

I even got another ATK for this new tank but decided not to use it (still in the box).
Also with the level sensor I find it’s better when it comes to chattering (repeated start/stop).
I’ve had to add a bunch more code on the ATK setup to prevent that.

I would think its the Water level sensor causing this issue - it could simply be that its not reacting fast enough to turn off the ATO pump and you are ultimately adding more fresh water to the tank each time, than is needed. Over time, this could begin to add up and slowly drop your salinity level.

If it where me (and this is how I run my ATOs) is i would run an independent ATO - a self contained system , separate from the Apex. There are lots of great option about there.

Then, set that up as the main driver of your ATO pump, but power it via an Apex outlet.

next, setup a secondary switch (float or optical) that sits higher than your main ATO sensor and run that through and monitor it with the apex (the FFM module if good for this). This secondary sensor will be the "High Water" mark, and used to monitor the function of the stand along ATO system.

Program the apex to simply turn off your ATO system if the "high water" sensor is triggered. It wont typically be trigged unless the main standalone ATO system malfunctions and dumps too much water.

This will help with drift AND isolate the Apex from from having full control of such important system, while also providing some monitoring redundancies.

You can still have you water level sensor in there and use it for information purposes or even use it as a third "High water" sensors to monitor the monitor that is monitoring the ATO.

On a side note - i would also like to see the temperature, overlayed on your salinity graph. Some of that regular swing in salinity could just be the variation caused by regular temperature swings that happen through the day.

 

[Alexr54]

I would think its the Water level sensor causing this issue - it could simply be that its not reacting fast enough to turn off the ATO pump and you are ultimately adding more fresh water to the tank each time, than is needed. Over time, this could begin to add up and slowly drop your salinity level.

If it where me (and this is how I run my ATOs) is i would run an independent ATO - a self contained system , separate from the Apex. There are lots of great option about there.

Then, set that up as the main driver of your ATO pump, but power it via an Apex outlet.

next, setup a secondary switch (float or optical) that sits higher than your main ATO sensor and run that through and monitor it with the apex (the FFM module if good for this). This secondary sensor will be the "High Water" mark, and used to monitor the function of the stand along ATO system.

Program the apex to simply turn off your ATO system if the "high water" sensor is triggered. It wont typically be trigged unless the main standalone ATO system malfunctions and dumps too much water.

This will help with drift AND isolate the Apex from from having full control of such important system, while also providing some monitoring redundancies.

You can still have you water level sensor in there and use it for information purposes or even use it as a third "High water" sensors to monitor the monitor that is monitoring the ATO.

On a side note - i would also like to see the temperature, overlayed on your salinity graph. Some of that regular swing in salinity could just be the variation caused by regular temperature swings that happen through the day.

I can understand your point. But if you look at the water level graph, its consistent. So when the water level sensor triggers the ATO it always shows the start and stop at the exact same levels. I would also think if what you are saying is the case this would eventually lead to an overflow situation.

My temp does not swing more then +-1°. I have a chiller hooked up.

 

[Vivid Creative Aquatics Verified Sponsor]

What is happening between these 12hr periods?

Is the ATO adding small amounts of water throughout this period to maintain level?

Or, is the ATO simply adding all the necessary fresh water once ever 12 hrs?

if it's once every 12 hours, then I would still lean towards the water level sensor being used to trigger the ATO as the issue. It could be as simple as variations in the sensors readings at the extremes (low/high water) which could affect when the ATO is trigged and thus how much water is added.

 

[Vivid Creative Aquatics Verified Sponsor]

Understood but what is the cause of the fluctuations I have 4 tanks running that don't fluctuate.

If all for tanks are running with the same sort of setup to maintain salinity - the next thing would consider is faulty equipment. It would be easy enough to test - you could swap the water level sensors between the tanks and see if the issue follows the sensor or stays with the tank.

 

[Grog]

OK a stupid question and idea.

Is your salinity tester directly next to where the RODI is being filled during the ATO operation?

If so, that particular area may be temporarily less saline due to the concentration of RODI in the zone.

Maybe move the probe to another spot in the tank? Even just to another area of the sump.

 

[Alexr54]

What is happening between these 12hr periods?

Is the ATO adding small amounts of water throughout this period to maintain level?

Or, is the ATO simply adding all the necessary fresh water once ever 12 hrs?

if it's once every 12 hours, then I would still lean towards the water level sensor being used to trigger the ATO as the issue. It could be as simple as variations in the sensors readings at the extremes (low/high water) which could affect when the ATO is trigged and thus how much water is added.

I have a zone valve (like used for irrigation) directly powered by the Apex controller (24v) which opens/closes water to my RODI based off this code in Apex for the Zone Valve power. So when my ATO runs, its not a huge stream, its just as fast as the RODI can produce the cleaned water. Its directly from my RODI to my refugium/sump in the same compartment with the return pump.
The salinity probe is in the compartment before the return pump and ATO fill hose. So the fresh water does not directly affect the salinity probe without first cycling through the tank.

Fallback OFF
Set OFF
If WtrLev < 6.5 Then ON
If WtrLev > 7.1 Then OFF
When On > 010:00 Then OFF
Defer 005:00 Then ON
If FeedA 006 Then OFF

With this code i have already attributed for any possible water level sensing lag. And based off the graph trends it is stable.

What you see in the water level sensor graph is pure water evaporation.