Salinity question...
- Thread starter Haroldeez
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RobW
Valuable Member
Rock will not soak up the salt. The rock is in the water column and the salt content is the salt content. You have something strange going on. What type of salt mix are you using?
Haroldeez
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red sea pro.... why I’m using pro I have no idea I don’t plan on corals till months and months from now. I’ve basically just been getting the most expensive of everything thinking it must be the best
00Barracuda00
Active Member
I would check the height of your optical sensor. If it is set too far above the waterline when your return pump is on, it may begin auto-filling.
Eliminating this possibility, I would then check the lines on the ATO. Do you have a siphon break installed? Is the pump slowly dripping water through the line when 'off'? The line could be siphoning the ATO out to a level of equilibrium within the tank, which would account for both the salinity drop and the high ATO output.
EDIT for clarity: I would check BOTH the pump on the ATO and the lines.
I would suggest calibrating it with a 35ppt solution. Years ago I used to use rodi water to calibrate mine and something always seemed off when making new water. I make 150-200 gallon batches, and it never took the same weight of salt to make a batch. Figured it was just the salt. Well it wasn't. I have been using the 35ppt solution and calibrate before any testing, and instead of using, say, 45 lbs to make 150 gallons, then 49 lbs, then 44 lbs. It stays at a consistent 46 lbs for example.
BeejReef
2500 Club Member
How often do you do water changes and how big? With my particular refractometer and salt mix, the salinity would measure 1.026 or 35 15 minutes after I made the batch, but then would measure a fair bit lower several hours later. I was doing 25% WC every week and always having to correct up salinity until I started making my salt water the day before WC day.
Another possibility (that also flummoxed me). How stable is the water level in your DT? My overflow is difficult to dial in. Sometimes it leans pretty heavy on the emergency overflow and the water level in the DT is pretty high. Other times, it seems to find a balance just above the main return pipe. Point being, your ATO can fill the sump to the "correct" level, but if your DT is running too high, you're increasing your total water volume (and decreasing salinity).
Another possibility (that also flummoxed me). How stable is the water level in your DT? My overflow is difficult to dial in. Sometimes it leans pretty heavy on the emergency overflow and the water level in the DT is pretty high. Other times, it seems to find a balance just above the main return pipe. Point being, your ATO can fill the sump to the "correct" level, but if your DT is running too high, you're increasing your total water volume (and decreasing salinity).
Retro Reefer
Slow and steady wins the race!
My guess is testing errors or faulty refractometer or both 
Haroldeez
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Ahhh yes the overflow box is VERY finicky with these... it seems just the slightest tap on the gate valve can make a huge difference and sometimes a large adjustment is needed to make a difference. I think this may be the right track to explore
I had a refractometer that I used to calibrate with RO water and I got by fine but it was always not 100%. I ordered a 35pt solution to calibrate and I calibrate prior to every test now. I started to notice that I was getting different readings after awhile i.e. fast drops in salinity or rises. Its prob time for me to buy a new refracto because it requires constant calibration now or will read low usually.
clm65
Well-Known Member
Ok, let's assume you have 30 gallons worth of rocks, sand, etc., and just work with the 70g DT volume. Dropping from 35 to 30 salinity is about a 14% reduction. I believe you can basically equate that to replacing 14% of your DT volume with fresh water, or 9.8 gallons. Since you would certainly see 9.8 gallons of water on the floor, and you said you are only adding 1 gallon per day or so, which is reasonable for evaporation, I am inclined to agree that you have an issue with your refractometer.
This is correct. You should always calibrate equipment close to the range of values that you will be testing. A refractometer calibrated at 0ppt might not be accurate around 35ppt since you're basically extrapolating.
00Barracuda00
Active Member
Having eliminated the ATO itself as the culprit, I believe we can now move on to the water change process itself.
How long are you waiting before taking readings? You might see falsely elevated salt levels in a mixture that isn't 100% mixed. In essence, you could be reading the right levels because the number of undissolved particulates indicates the desired mix. Over time, as those last bits of salt become part of the solution, you'd get much lower readings.
As posted above, it would also be wise to double check the calibration of your refractometer against the manufacturer's instructions.
How long are you waiting before taking readings? You might see falsely elevated salt levels in a mixture that isn't 100% mixed. In essence, you could be reading the right levels because the number of undissolved particulates indicates the desired mix. Over time, as those last bits of salt become part of the solution, you'd get much lower readings.
As posted above, it would also be wise to double check the calibration of your refractometer against the manufacturer's instructions.
