ATO lowering salinity?

[Mikemont1991]

Hey all. I’m about 4 months in, got some fish and corals in my RS MAX Nano—they all seem to be doing fairly well, no major trouble I couldn’t fix. I do notice that my salinity is consistently hard to keep up; I guess it was wishful thinking that my water would evaporate and be replaced by the ATO at a rate that would keep salinity consistent, but I find over a few weeks ill drop several points when I’m just filling the ATO with RODI - Is this normal?


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[bg2311]

Are you also doing water changes?

 

[Mikemont1991]

Are you also doing water changes?

I am, at least 5 gal every 1-2 weeks


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[york1]

Are you sure your ATO is working properly?

 

[bg2311]

Not familiar with the tank model. What's the total system volume? 5 gallons might be a lot or a little depending on the size. How are you measuring salinity? If it's with a refractometer, make sure it's calibrated against a known value like calibration fluid and don't forget to correct for temperature.

Here's a page I like to use that lets you quickly correct for observed vs actual salinity based on the water temperature.

Salinity Correction Calculator

Aquarium calculator; Correct a relative specific gravity (sg) measurement taken with a non-temperature-correcting unit.

www.hamzasreef.com

 

[Mikemont1991]

Are you sure your ATO is working properly?

It’s just the “hang on back” one that came with the aio tank so I’m sure it’s not the best. I guess maybe the water level in the rear “sump” could be giving me issues? AIO tanks are cool but I wish I had a full sump sometimes to see what’s going on


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[york1]

It’s just the “hang on back” one that came with the aio tank so I’m sure it’s not the best. I guess maybe the water level in the rear “sump” could be giving me issues? AIO tanks are cool but I wish I had a full sump sometimes to see what’s going on


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The ato for my redsea 250 is sitting out in the garage collecting dust. For small tanks I like Autoaqua smart ato micro.

 

[Mikemont1991]

Not familiar with the tank model. What's the total system volume? 5 gallons might be a lot or a little depending on the size. How are you measuring salinity? If it's with a refractometer, make sure it's calibrated against a known value like calibration fluid and don't forget to correct for temperature.

Here's a page I like to use that lets you quickly correct for observed vs actual salinity based on the water temperature.

Salinity Correction Calculator

Aquarium calculator; Correct a relative specific gravity (sg) measurement taken with a non-temperature-correcting unit.

www.hamzasreef.com

Thanks, it’s 20 gallons total so not huge. Since it’s so small I’m using store bought water for the changes—I do test it before the change and it comes in at 1.026 every time


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[Steve Burton]

The ATO should not change salinity as long as it is only filling the water that evaporates. Ditto for water changes if your change water is the exact same salinity. Could it be possible that you're accidentally taking out more than you add, the ATO could be making up the difference. That could happen if the ATO is overfilling then you only refill to the real line on water changes.

 

[Mikemont1991]

The ato for my redsea 250 is sitting out in the garage collecting dust. For small tanks I like Autoaqua smart ato micro.

Yeah I’ve meant to replace it just hadn’t pulled the trigger yet - anything better about the autoaqua above the tunze? I’ve heard people suggest both


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[bg2311]

Thanks, it’s 20 gallons total so not huge. Since it’s so small I’m using store bought water for the changes—I do test it before the change and it comes in at 1.026 every time


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How much of a drop in salinity are you seeing and over how long?

 

[Mikemont1991]

The ATO should not change salinity as long as it is only filling the water that evaporates. Ditto for water changes if your change water is the exact same salinity. Could it be possible that you're accidentally taking out more than you add, the ATO could be making up the difference.

It’s possible, I try to match it but I’m sure it’s not perfect


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[Mikemont1991]

How much of a drop in salinity are you seeing and over how long?

I checked today and it’s 1.022, I haven’t done anything besides fill the ATO in 2 weeks


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[bg2311]

Do you have a skimmer? Emptying the cup will cause the ATO to run more. As salt water in the cup is removed and replaced by fresh water the salinity will drop. If not, something to keep in mind in the future.

 

[york1]

Yeah I’ve meant to replace it just hadn’t pulled the trigger yet - anything better about the autoaqua above the tunze? I’ve heard people suggest both


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I use both. I use the tunze 3155 on all my big tanks and micro on my smaller tanks

 

[Mikemont1991]

Do you have a skimmer? Emptying the cup will cause the ATO to run more. As salt water in the cup is removed and replaced by fresh water the salinity will drop. If not, something to keep in mind in the future.

That’s a good point, it is a small skimmer that’s in the back as well—I run it all day/night usually and empty it every couple of weeks


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[bg2311]

That’s a good point, it is a small skimmer that’s in the back as well—I run it all day/night usually and empty it every couple of weeks


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If it's that small a volume being removed and that infrequent it shouldn't affect salinity as much as you are observing. How are you measuring it? Refractometer?

 

[Mikemont1991]

If it's that small a volume being removed and that infrequent it shouldn't affect salinity as much as you are observing. How are you measuring it? Refractometer?

Yes, the Red Sea refractometer. I’ve thought about just getting another one in case it’s a bad model—feel like I’m taking crazy pills


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[bg2311]

Yes, the Red Sea refractometer. I’ve thought about just getting another one in case it’s a bad model—feel like I’m taking crazy pills


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A digital one is on my shopping list. There's a calibration set screw normally. If in doubt, can test it with some calibration fluid that is a known salinity to confirm it's reading or if it needs adjustment. Again, even calibrated the scope ones like that don't correct for temperature. The same water at different temps will give you different salinity readings on a refractometer.

 

[Mikemont1991]

A digital one is on my shopping list. There's a calibration set screw normally. If in doubt, can test it with some calibration fluid that is a known salinity to confirm it's reading or if it needs adjustment. Again, even calibrated the scope ones like that don't correct for temperature. The same water at different temps will give you different salinity readings on a refractometer.

Good to know — thanks for the help


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