Tank water level has me BEYOND confused

[Felix T Cat]

So I just set up my 90 in the apartment. I have a 12g top off tank and had the tank up and running for about 3 weeks. Lighting is an Outer Orbit 2x250 MH and 4x T5. Salinity was 1.024 after my last water change. During the 3 weeks top off was about 5-7 g a week although I always keep the windows open.

I left on business for 5 1/2 days. When I got home saturday the top off tank was empty and the tank was down a good 5-6 inches from the top. I immediately started making RO/DI water but when I checked salinity it was 1.026 ?

I got the tank level back up about 3 inches and now salinity is 1.021. I still need about another 2" of tank fill but I'm trying to figure out what happened ?. My first thought was excessive evap because the apartment was closed up for 5 days but then I would have expected the salinity to be much higher and would have expected to be able to refill the tank and get back to 1.024.

I'm mixing some new water and plan on topping off the tank to get the salinity back up a few points and I will apparently have to get a glass top before my next long trip.

It's seriously like someone came in and took 15g of water out of the tank. There are no leaks, no signs of water on the floor or anywhere.

Thoughts ?

 

[carey]

I'd put my money on evaporation. I replace over a gallon a day in my 125g. Those halides can cause excessive evaporation as well.

As long as there were no leaks that you can find I wouldn't worry too much about it.

 

[joy13]

Make sure you don't change your SG to fast. Instead of using fresh water in your top off just use the 1.025 or what every you run so that it doesn't change to rapid. Are you using a refractometer or a hydrometer to measure your SG?

 

[adeebm]

Evaporation won't take the salt with it. So either you're measurements aren't accurate or there was a leak or some sort of accident. That is very strange if there's no sign of leakage.

--Adeeb

 

[Felix T Cat]

Using refract and I have 2 of them that I have used for a while, checked with both (they differed by .001 but close enough in my book).

The salinity is the part that's confusing the **** out of me. I mean I know that a closed house will cause higher rates of evap but I would have expected the salinity to go up and then I would refill with fresh water and it would be all good.

 

[MikeYQM]

Are both refractometers calibrated at room temp with RODI water? Temp of the Refractometer can make them very inaccurate. If its not a leak, it's user error.

 

[Felix T Cat]

Both were done with RODI with fresh made water (I double checked them both this morning). Maybe I'll make some water and let it sit for a while to get to room temp and double check them.
I've gone around the tank numerous times and for once being a not so uber clean person has paid off. There is a small amount of dust that would have shown water if any had leaked. (especially that much)

 

[Felix T Cat]

Side note: new mixed water shows 1.025 on refract.......still completely confused and looking for a leak somewhere.

 

[kurtyboh]

even a leak wouldnt change sg...

 

[crister13]

Ya I would guess evaporation. Are you topping off with salt water? If you are, saltwater doesnt evaporate and that couldve done it.

 

[crister13]

Sorry, SALT doesnt evaporate.

 

[MikeYQM]

My bet is user error in testing. Not pointing fingers but no other option seems logical. Keep monitoring with calibrated gear & you should be fine. If you find something else, share your info!

 

[paulweck]

I don't know if I missed it in another thread but have u looked around for any salt creep. That the only way your SG will drop. The reason I think it dropped to 1.021 is from filling so much ro/Di to top off and u need to give the tank a few hours to mix before u test the SG. I would suggest like sombody else did never top off more then a gallon a day. It needs to be countionus through the day to show no effect in your SG

 

[Felix T Cat]

My top off container is filled with fresh RO/DI water (never had salt in there). I understand why it dropped to .021 but I had to get my tank level back up for the skimmer and hang on fuge. I've unplugged my ATO and mixed up 5 gallons of new salt water which I plan on slowly using to bring sg back up until this weekend when I can do a larger water change.

I have completely wiped down the tank and will be looking for any signs of salt creep over the next week or so while I'm going to be local. I also ordered glass tops to minimize evap when I travel for longer periods of time in the future.

I swear if I didn't know better I would say someone came in and borrowed 15 gallons of water from the tank.

I've been doing reef tanks for over 3 years now (with most of the same equipment) so while I'm not ruling out a possible "jack daniels" moment during my last measurement I'm still stumped.