Salinity change as ATO replaces water

[Mz. Fix It]

I have always liked the salinity in my tank to be in the 35 range. What I have found with my ATO is that over time my salinity begins to decline and is currently down to 32. This has bothered me so two weeks ago I turned off the ATO and started adding water manually daily but instead of fresh RODI water as the top off I have used my saltwater mixture. Over the past two weeks my salinity has slowly climbed up to 34.2 as of today. I have an Apex so I watch my salinity ongoing and it appears this slow addition of saltwater has been the answer to getting my salinity back to the place I like to keep it. However, from here moving forward I'm a bit perplexed on the best solution to keep my salinity up where I want it to be. If I continue to top off with saltwater my salinity will begin to get too high....I'm assuming.....but if I go back to using the RODI water.....once again my salinity is going to start to drop again.....I'm assuming.

I also have an AWC setup, however, I have not had it on for the past two weeks in hopes of getting my salinity back up where I want it to be. Could it be the daily small water changes that is causing the decline in salinity? It wouldn't make sense in my head because the water is constantly being replaced with 35 salinity water in the AWC.

Could it be the lack of water changes over this past two weeks and only topping off each day that has helped the salinity start to get back up where I want it to be?

My ATO reservoir is 20 gallons. Normally in two weeks although it's not completely empty it's low enough that I need to start to refill the reservoir before the pump starts to have an issue. So in my mind using approximately 18 to 19 gallons of RODI water over a two week period is a big contributing factor for the salinity dropping.

For clarification I have a Red Sea 525 XL that has a DT of 108 gallons and a sump with 31 gallons and a 5 gallon refugium that sits above the sump (originally Red Sea intended for the 5 gallon tank to be used as the ATO reservoir but I made it my fuge and set up an exterior 20 gallon ATO reservoir).

My tank has been running 8 months and I have mainly LPS corals, CUC, fish and some stars. Any advice anyone has about my desire to keep my salinity up around 35 ongoing will be greatly appreciated.

For the record.....many fellow hobbyist told me that keeping a salt tank was just as easy as my freshwater tanks....it was just going to cost more money. They were wrong.....I LOVE my tank and it's inhabitants.....but it's ALWAYS something or the other going wrong or something dying for no apparent reason. I have the Trident and ReefBot testers and my parameters seem to stay in line without any major spikes one way or the other.....but corals doing great one day.....next day.....dead as a door nail. Fish....don't even get me started there. THANKFULLY, as I knock on every wood object I can find around me, I have not experienced ick in my salt tank.....have had it numerous times in my freshwater tanks....and was told it was not if I got it in my salt tank....but when.....hopefully that won't be my situation since I've limped along this long without it. I won't even discuss the cost.....absolutely and painfully expensive....but I'm OCD and MUST have every gadget...LOL. Perhaps once my salt tank has been running for a year or two the challenges will be few and far between.....hopefully......my freshwater tanks have always been super easy....I could fill their tanks up with swamp water/toilet water or any other variation of water and they'd be fine......fresh guys are super hardy IMHO. Salt.....not so much....and certainly not "as easy" as fresh!!!...they lied to me! LOL

 

[Randy Holmes-Farley]

Yes, an AWC will cause changes in salinity if not exactly matched in volume.

Also, skimming reduces salinity. How much obviously depnds on the amount of skimmate collected. It has roughly seawater salinity.

 

[kevin_e]

I'd be more focused on the saltwater from your autowater change. I would also look into verifying your probe or calibrating it. A drop in salinity from an ATO seems unlikely to me.

 

[Idoc]

Another common source of a slight reduction in the salinity --- As you empty your skimmer cup, that slight reduction causes a slight reduction in the tank's water volume that is then filled by freshwater RODI water. Overtime, this adding freshwater to replace saltwater volume will slowly reduce your salinity...especially if skimming wet. Just a thought....

 

[Mz. Fix It]

Yes, an AWC will cause changes in salinity if not exactly matched in volume.

Also, skimming reduces salinity. How much obviously depnds on the amount of skimmate collected. It has roughly seawater salinity.

The AWC reservoir I keep higher for this exact reason. Instead of 35 I keep it at 36 and I see the salinity going up on the reservoir as the week progresses. I've been keeping the reservoir salinity higher in hopes of "naturally" increasing the salinity in my tank...but it hasn't really helped.

My skimmer cup fills and I empty it about once a week.

 

[Mz. Fix It]

I'd be more focused on the saltwater from your autowater change. I would also look into verifying your probe or calibrating it. A drop in salinity from an ATO seems unlikely to me.

As I mentioned above, I am keeping the salinity in my AWC reservoir higher, between 36 and 37, in hopes of "naturally" keeping my salinity up to 35 like I prefer but that hasn't worked yet.

I have calibrated all my probes several times over the past few weeks in hopes of solving this challenge. I'm not sure what you mean by verifying? I'm assuming you mean check it against another tester? I have a Hanna tester and I have rechecked with it and even recalibrated the Hanna tester to make sure I am getting accurate readings.

 

[Mz. Fix It]

Another common source of a slight reduction in the salinity --- As you empty your skimmer cup, that slight reduction causes a slight reduction in the tank's water volume that is then filled by freshwater RODI water. Overtime, this adding freshwater to replace saltwater volume will slowly reduce your salinity...especially if skimming wet. Just a thought....

Idoc, I empty my skimmer cup about once a week. Yes, if I was running it wet and emptying it several times a week I suppose I could see a slight decrease in salinity. However, I must admit.....I'm still stumped by this whole skimmer concept and what is the "best" way to set it up to run so I suppose I run it leaner than some. I've been told by my fellow hobbyist friends to turn the skimmer off to let your nutrients build up....turn your skimmer on because it's what we all do....turn it on...turn it off.....turn this knob...turn that knob....I don't fully understand what I'm doing with the whole skimmer thing but I do know I don't empty it that often so I'm not pouring off lots of water several times a week.....I also know one skimmer that cost me $600 range doesn't help me understand it any better than the one I just paid $500 for.....they are a total PITA IMHO. But....that's a story for another post...LOL

 

[Copingwithpods]

Generally speaking we lose small amounts of salt from skimming, saltcreep, testing, fragging and so on. These are small amounts that add up over time.

As you have an AWC that would be my first suspect. It is probably pulling more water out than it is putting in. Which one are you using and does it shut off your ATO while performing the water change?

An ATO alone will not decrease your Salinity unless your physical water level is increasing over time or you have a leak somewhere.

I would look to calibrate your AWC first and make absolutely sure that the x amount going out matches the x amount going in.

 

[Mz. Fix It]

Yes, an AWC will cause changes in salinity if not exactly matched in volume.

Also, skimming reduces salinity. How much obviously depnds on the amount of skimmate collected. It has roughly seawater salinity.

Randy Holmes-Farley - I forgot to mention earlier that I use the Apex DOS to do my AWC.....so in "theory" the amount removed and the amount added back in during the AWC should be exact.....at least that's what I understood when I bought this incredibly expensive piece of machinery to do the daunting task of water changes.

 

[Copingwithpods]

Randy Holmes-Farley - I forgot to mention earlier that I use the Apex DOS to do my AWC.....so in "theory" the amount removed and the amount added back in during the AWC should be exact.....at least that's what I understood when I bought this incredibly expensive piece of machinery to do the daunting task of water changes.

Never assume, verify for yourself. Expensive doesn't mean it can just be blindly trusted.

 

[Mz. Fix It]

Generally speaking we lose small amounts of salt from skimming, saltcreep, testing, fragging and so on. These are small amounts that add up over time.

As you have an AWC that would be my first suspect. It is probably pulling more water out than it is putting in. Which one are you using and does it shut off your ATO while performing the water change?

An ATO alone will not decrease your Salinity unless your physical water level is increasing over time or you have a leak somewhere.

I would look to calibrate your AWC first and make absolutely sure that the x amount going out matches the x amount going in.

Copingwithpods - I am using the Apex DOS to do my AWC's. It's interesting that you should ask about the ATO going off during the AWC's. Initially I had the AWC running with the remove and add running at the same time so there was no need to turn off the ATO. However, then I decided to change over to doing the removal first then the add later after reading discussions about doing them simultaneously makes no sense to some. Although I would LOVE to know how to program this $%@*#+% Apex to turn off the ATO for me during AWC's, I cannot do so, which has required me to set a calendar reminder for each day to go into my Apex and manually turn off the ATO then go back in and turn it back on. A true PITA since I have way too much money invested in all of this equipment that should do this for me.....but I just cannot figure out that stupid coding crap on Apex so manual turn off it is. My point being.....I have never had the remove side running and the ATO being on.....in essence filling the tank with RODI instead of the intended salt replacement....so I know that's not the culprit.

 

[SPSReeferMI]

I have a very similar set up. I notice that I’m usually lower in salinity after a couple of weeks. I too have the trident, Reefbot, skimmer, AWC.

Keep in mind that trident and Reefbot pull samples out. Per test, the trident pulls less, but it likely performs more tests every day. I’ve read that the Reefbot can pull out quite a bit of your tank’s water each test.

I’d make sure that you calibrate your Dos. I double checked mine for exactly this reason.

My current solution is that I usually add 100-250ml more New Salt Water per day in my AWC settings.

Finally, make sure that you are using a good tool to measure salinity.

 

[Randy Holmes-Farley]

Idoc, I empty my skimmer cup about once a week. Yes, if I was running it wet and emptying it several times a week I suppose I could see a slight decrease in salinity. However, I must admit.....I'm still stumped by this whole skimmer concept and what is the "best" way to set it up to run so I suppose I run it leaner than some. I've been told by my fellow hobbyist friends to turn the skimmer off to let your nutrients build up....turn your skimmer on because it's what we all do....turn it on...turn it off.....turn this knob...turn that knob....I don't fully understand what I'm doing with the whole skimmer thing but I do know I don't empty it that often so I'm not pouring off lots of water several times a week.....I also know one skimmer that cost me $600 range doesn't help me understand it any better than the one I just paid $500 for.....they are a total PITA IMHO. But....that's a story for another post...LOL

i would skim for the aeration benefits alone.

 

[Mz. Fix It]

Looking over old posts and saw this one. Wow.....a lot has changed since I made this post. Thankfully I have been able to figure out, with some help from the Neptune community forum, how to program my Apex to turn off my ATO during my water changes. What I have also realized after much calibrating, testing, calibrating again, retesting again....and staying on this hamster wheel until I was ready to pull my hair out is that no matter how many times I calibrate my DOS pumps....daily even.....it gives me a different reading, never consistently 40 ml after calibration. After letting my AWC run for a few days and having the ATO come on about an hour after everything stops I also realized that consistently that either the DOS adds less than it takes out....or.....somehow within two hours of water changing that at least a pint evaporates (unlikely IMHO). I have tweaked and tweaked over the past few months and have resigned to the idea of adding a pint more each day than I am removing. Salinity is staying steady so I feel confident that was the challenge originally when my salinity kept dropping each week.

Also since my initial post I have chosen to breath and stop chasing numbers. I have had to repair several things on my ReefBot...sadly....but as of now it's working but gives me inconsistent (compared to Trident and Hanna testers) results....but at least it's consistently inconsistent so I know my numbers are at least steady....just maybe not at the reading number the bot is telling me. Trident isn't perfect either.....but same with it.....it's consistently inconsistent so I know I'm staying steady on the course. And of course the biggie....fish and corals aren't dying anymore.....growing like weeds actually.....so after stumbling over many hurdles, losing more money than I care to speak of due to losses....for now I'm steady as she goes......for now.....but it's a salt tank....so it may change tomorrow. (LOL)

 

[choss]

I'm glad I found this post. I also have an AWC system (litermeter 3 - calibrated), a GHL ALK tester (which drains small samples daily), and a Tunze ATO which has traditionally been very accurate. I see my salinity drop a bit every week. At one point I was able to trace the drop to tiny leaks in the plumbing, but i fixed these and the salinity still drops slightly. I have tried to offset via AWC water (adding at 36 or 37) but I haven't yet achieved the right balance. Out of curiosity do wonder how much Skimmers, testers, and general salt creep impact 100 gallon+ systems