Salinity dropping?

[ketchup318]

Hi

I've had a strange trend occurring the past few months, tipped off by my corals lack of growth and eventual shrinkage. My tank's salinity levels are dropping and I don't know where it's happening.

So, rewind a few months back. My tank's already been setup, but I add my first coral, a Pom Pom Xenia. I check all the levels and salinity, PH, etc and make sure everything's fine, and everything grows fine. Then I notice the Xenia starting to recede a little, after a few months. I check everything again, and the salinity is low, from 1.026 to 1.020. I fix it, and everything's fine again.

Fast forward to last week, and the same thing happens. I do have a top off system, but it only refills when the fuge is low. When I do WCs, the salinity is 1.026, and I refill the tank back to the same level.

So if only evaporation is occuring, and pure water is going back, everything should be in balance, right? And if I refill with the same salinity back to the same tank level, the ATO isn't upsetting the salinity levels...

Just wondering if there's anything else that could cause the salt levels to drop... thanks

 

[BigRedsReefs10]

If your getting excessive salt creep that can cause your salinity to fall, but .006 is a lot

Edit: your not using an air stone are you?

 

[Breakthecycle2]

How are you checking the salinity? What are you using?

 

[mrvincent]

If you check salinity of the new water straight after you mixed it with salt, you'll get higer values, and when you mix it with the tank water it will drop.

Check if you don't have a leak somewhere... The only way to drop salinity is to remove salt. To remove salt you must remove salted water. Splashes/leaks will remove salted water and your topoff will compensate with pure water, so the salinity will drop.

To get huge drops like this you probably have a leak somewhere... Search for salt creeps...

 

[ketchup318]

Thanks for all the responses. I'm not using an air stone nor do I have excessive salt creep. I am using a refractometer for both the mixed saltwater and the tank water, so they're both calibrated to the same source. The tank is on hardwood so it should be pretty evident if there was a continuous leak.

What you said about the freshly mixed water dropping in salinity is intriguing. How long should you let the mixed saltwater sit for? I usually just mix it for around and hour. It's pretty warm here in California, so when the water clears, particles settle and the water hits 78F, it goes straight into the tank.

 

[BigRedsReefs10]

You should mix it for about 24 hours for most salts. Rscp recommends 4 hours but I still do 24

 

[Breakthecycle2]

Have you checked the calibration with R/O water? My refractometer needs to be re-calibrated every few weeks for some reason. It's usually off between .02-.04

 

[mrvincent]

What you said about the freshly mixed water dropping in salinity is intriguing. How long should you let the mixed saltwater sit for?

That's because I use a densimeter and not a refractometer. They're behaviours are differents while mixing salts. After 1 hour I can get accurate salinity, but I don't know if it's the same with refractometers...

Folks here told me to mix is 24 hrs, but I have no problem to put it in the tank after 3-4 hours. I have mesured levels (Ca, KH, Mg) straight after adding new mixed water, and I get same results 48 hrs after.

Adding it to the tank after 1-3 hrs may create microbubbles problem for few hours and/or pale white cloudy water, but that's not a problem I think. As long the corals stay healthy...



Maybe you have refractometers problem... Try using a cheap densimeter (available in home brewing beer/wine shops).


I know it's not the most accurate, but I use this for mesurements, it needs no calibration:

I always get same values for both with this:

Mine is way more accurate than this small one on the second picture.

 

[herp_mommy]

Have you checked the calibration with R/O water? My refractometer needs to be re-calibrated every few weeks for some reason. It's usually off between .02-.04

This. I re-calibrate my refractometer every few weeks. Make sure you're also cleaning it with ro/di after you use it and put it away. It can really affect your readings.

 

[TheTodd]

Good advice on checking your refractometer.

Hydrometers don't need calibration, but you would be lucky to get one that is accurate. I had one and got two that came with my 240g. All three read different levels using the same water and none match my refractometer. Probably not a huge issue in a FOWLR, but I would want some precision in a reef.

 

[ketchup318]

I'm using the same instrument to test the mixed incoming water and the current tank water. If the baseline calibration is off, it'll be off for both. What I'm seeing is a relative difference between the two, which indicates it's not a simple calibration issue. That said, I'll check and recalibrate the refractometer, it's always a good idea to have it calibrated.

I'll also run a test to see if the mix duration makes a difference, with my current setup.

 

[BigRedsReefs10]

It sounds like your testing the salinity before it's completely dissolved. I usually get a good reading about 8-10 hours after mixing. I'll make it in the morning, check the salinity that night and do the wc the following day

 

[jeffaquarius]

How often does your skimmer gets full? The question sounds unrelated but your salinity gradually goes down every time your skimmer gets full.

 

[ketchup318]

I thought about the skimmer too, but I only dump out a 1/2 cup every few days.

 

[jeffaquarius]

I also use refractometer and lately I have to calibrate it twice in a week. You also need to be aware that the temperature of saltmix will affect the salinity readings. There are refractomers that do not have the temperature compensation feature. I also agree that 1 hr after mixing is not a good idea. The salt will not be evenly distributed and you will get high readings on top even you have circulating pump on your container.