My salt level is dropping?

[Monica]

My salt level is dropping in my 10 gallon tank. Yesterday it was 1.021, today it is 1.019. Why would it be dropping? Could the filter be removing the salt? I'm worried about my fish, any ideas?

[MKramer]

I'm assuming you haven't topped off with any water between those readings. There are two possibilities that I can think of:

 

1) Temperature. You're measuring the density of the water, which changes with temperature, as well as salt content. So even if your salinity is the same, but your water was warmer duringt he second reading than the first, it would be less dense, and therefor read lower.

 

2) Hydrometer. These things are pieces of junk, and I've never met a hydrometer that I've liked. Even if they give consistent readings, they're usually off-the-mark. And the slightest little air bubbled or deposits will cause them to give varied readings.

 

I'd worry about it only if it continues to fall. You can take your water to an LFS who can test using a refractometer or electronic probe, and compare it to your hydrometer reading fo the same water, to determine about how far off your reading is.

 

For a reef tank, I suggest shooting for 1.023-1.026 in the 80-83 degree range.

 

If you find your hydrometer is just giving inconcsistent readings, I'd replace it with another one. The most important thing about salinity is to keep it constant, and it's ahrd to do that if your meauring tool gives you a different result every time.

[Monica]

I didn't realize that temp. would be a factor. The temp. stays around 78. I have a floating hydrometer. My understanding is that when you top it off with water that you only use freshwater because the salt does not evaporate. Is this correct? Also I have no live rock or corals, I only have live sand. Thanks for your help.

[MKramer]

You are correct about the freshwater for top-offs. However, sometimes when I feed my critters, take them out for treatment or quarantine, or pack up a coral frag for another reefer, I have to remove water. That water must be replaced with saltwater, because the salt came out with it. I keep a gallon jug of freshwater and one of saltwater under my aquarium and use them appropriately. Salinity is about the only thing I ever test for, and I do it quite often.

 

Good luck with your setup. I'm sure this salinity thing will work itself out. It doesn't sound like there's any legitimate reason for the salinity to actually drop, so it's most likely just a measurement problem.

[harbingerofthefish]

I ran my tank with water and sand oly for a couple of days to check everything out. The first day I left the cover off the wter and the splash resulted in a roughly 10% water loss as well as a big drop in salinity.

 

Just a thought that it may be due to salt creep or the splash in your tank.