Salinity drop due to ATO?

[Cheeze]

Is it normal for salinity to drop from auto top offs?

My salinity has gone from 1.025 to 1.022 in about 2-3 weeks, and I don't see any leaks anywhere (living in an apartment, I would definitely notice leaks).
I'm using an ATO that I estimate adds back about a 1/2 - 3/4 quarts of RODI fresh water a day from a reservoir I set up. Finding very little salt crust in the AIO chambers and around the tank/rims, which I try to put back into the tank as much of as possible.

Here's some more info if it helps:
- 38 gallon AIO, newly set up less than a month ago with dry sand and dry macro rock
- Currently fishless cycling so I haven't done any water changes yet
- Using a refractometer to measure salinity every few days, also checking to make sure it's still calibrated
- Only running the return pump, wavemaker and heater. Lights have been off, and the skimmer is in the chamber but haven't used at all yet
- Temp has been a consistent 76 degrees F (checked daily)

I do pull out about 21 ml of water every other day to test ammonia and nitrites, which I've been doing for 2 weeks (so about 8 x's = 6 ounces I've removed for testing)

Could the drop be from the cycle process, or the water testing? Or is there just too much evaporation or fresh water going back in? Or are the reef elves stealing salt from my tank while I sleep?

 

[Jekyl]

ATO won't lower your salinity. Are you heating your new water before changes? Depending on test method it can change. How long are you mixing for?

 

[MichaelReefer]

Do you have a skimmer? Skimmer pulls out salt water, not fresh water. So over time it will deplete salt because its being replaced with just RODI.

 

[Cheeze]

Haven't done any water changes yet since I'm cycling, same water that went in 3 weeks ago.

And I haven't turned on the skimmer, at all. It's in one of my AIO chambers but never been used.

 

[Garf]

Reef Elves are recalibrating your refractometer with RODI probably, instead of 35ppt calibration standard.

 

[Jekyl]

How did you get your initial water?

 

[Cheeze]

Reef Elves are recalibrating your refractometer with RODI probably, instead of 35ppt calibration standard.

LOL...I have been using RODI to calibrate my refractometer, but aren't I supposed to?

 

[Saltyreef]

Ato could lower salinity if the reservoir continues to siphon into the tank unknowingly until equalized.
Easy to do in an AIO if the reservoir is level with tank.

 

[Garf]

LOL...I have been using RODI to calibrate my refractometer, but aren't I supposed to?

No

 

[Cheeze]

How did you get your initial water?

Made it myself via 5 stage RODI system, using water from the tap. Mixed Tropic Marin Pro Reef salt and the original salinity after a couple of days in the tank with the heater on was 1.025.

 

[Cheeze]

Ato could lower salinity if the reservoir continues to siphon into the tank unknowingly until equalized.
Easy to do in an AIO if the reservoir is level with tank.

My reservoir is on the floor below the tank level. The sensor is in the last 3rd chamber of the AIO where I've seen the water level drop from evaporation.

 

[Cheeze]

No

Re-read the instructions...I see I need to use distilled water to calibrate, which I did before first use but not subsequent. Although I also haven't had to adjust the calibration since I checked before first use.

 

[Jekyl]

Re-read the instructions...I see I need to use distilled water to calibrate, which I did before first use but not subsequent. Although I also haven't had to adjust the calibration since I checked before first use.

Mine came with calibration liquid. I'd get some if I were you. I calibrate every time I use it and it changes almost every time. The liquid I have calibrates to 35ppt

 

[Garf]

Re-read the instructions...I see I need to use distilled water to calibrate, which I did before first use but not subsequent. Although I also haven't had to adjust the calibration since I checked before first use.

There’s a simple DIY recipe from Randy Holmes Farley on here somewhere, using table salt and RODI. You’ll find your salinity is not what you think it is.

 

[NeonRabbit221B]

Is the end of the ATO line near the surface of the water? Sounds like you are back siphoning. Quick check is to check salinity of ATO reservoir. I also have seen a slow drip out of the tank from a dosing pump where the outlet is lower than the inlet. I have also see water wick its way out through a thread I had hanging into the tank... for some reason. I would be looking around the tank to see if SW is leaving the tank in some manner or going back into the ATO reservoir.

Or you can calibrate refractometers again idk

 

[Azedenkae]

Is it normal for salinity to drop from auto top offs?

My salinity has gone from 1.025 to 1.022 in about 2-3 weeks, and I don't see any leaks anywhere (living in an apartment, I would definitely notice leaks).
I'm using an ATO that I estimate adds back about a 1/2 - 3/4 quarts of RODI fresh water a day from a reservoir I set up. Finding very little salt crust in the AIO chambers and around the tank/rims, which I try to put back into the tank as much of as possible.

Here's some more info if it helps:
- 38 gallon AIO, newly set up less than a month ago with dry sand and dry macro rock
- Currently fishless cycling so I haven't done any water changes yet
- Using a refractometer to measure salinity every few days, also checking to make sure it's still calibrated
- Only running the return pump, wavemaker and heater. Lights have been off, and the skimmer is in the chamber but haven't used at all yet
- Temp has been a consistent 76 degrees F (checked daily)

I do pull out about 21 ml of water every other day to test ammonia and nitrites, which I've been doing for 2 weeks (so about 8 x's = 6 ounces I've removed for testing)

Could the drop be from the cycle process, or the water testing? Or is there just too much evaporation or fresh water going back in? Or are the reef elves stealing salt from my tank while I sleep?

The water testing would not have caused that drop in salinity. 21ml a day over 2 weeks amounts to 294 ml, which is like 0.2% of the water, so yeah.

ATO top off will not change the salinity, provided you measure salinity at exactly the same volume of water each time. Let say you have a baseline water level when you measured 1.025, lower water levels would see higher readings, and vice versa. ATO only replaces the water the has evaporated, so no removal of salt. So if you measure at the same water level as when you measured 1.025, you should still measure 1.025.

The only possibilities then are:
1. The water level when you measured 1.022 is higher than when you measured 1.025, i.e. you have somehow added to the volume of the tank wish fresh water, hence the concentration of salt has decreased and thus a lower reading.
2. You have lost so much salt to have gone from 1.025 to 1.022. Very unlikely, especially with a 38 gallon AIO.
3. You splashed so much water out of the tank that you are removing significant amounts of salt water replaced by fresh water from your ATO. Honestly, still pretty unlikely.
4. Refractometer issue.

I'd say the most likely possibilities are either there is a refractometer issue, or that you have ended up with more water in the tank now than you originally did from the ATO, somehow (perhaps where you placed the sensor or whatever has caused the ATO to add more water than was lost from evaporation).