What can cause a Salinity Spike?

JimDog2015 · Nov 21, 2015

Our 120 gal tank is in the middle of cycle, all levels looked normal, but yesterday our salinity jumped from 34 to 38 for no apparent reason. Now this morning the level is back to normal (34).

We have only been toping off with clean RO/DI water, so I'm not sure where that spike came from.
We have live sand, and rock that has been in the tank for at least a month and a half.
Diatoms are blooming a bit.
No other visible life.

So I have two questions;
> What can cause the spike?
> Should I be concerned that then we finally add livestock, if that sort of spike happens again?

Thanks

xmas_one · Nov 21, 2015

Sounds more like a testing anomaly to me.

Downbeach · Nov 21, 2015

If you're using a swing arm type hydrometer, it could've been micro bubbles on the arm. I would suggest getting a ATC refractometer along with a bottle of 35ppt calibration solution on your wish list.

mtfish · Nov 21, 2015

What are you using to test salinity. This is a physical parameter and cannot go up or down without either evaporation making it higher or added fresh water to make it lower. If you are using a conductivity probe, it could be electrical interference. If you are using a swing hydrometer, they can vary with user misuse. A refactometer is usually a stable instrument if it is properly calibrated.

Randy Holmes-Farley · Nov 21, 2015

To get there by evaporation would require about 12% of the water to evaporate, or a bit under 3" in a 24" deep aquarium.

JimDog2015 · Nov 21, 2015

mtfish said:
What are you using to test salinity. This is a physical parameter and cannot go up or down without either evaporation making it higher or added fresh water to make it lower. If you are using a conductivity probe, it could be electrical interference. If you are using a swing hydrometer, they can vary with user misuse. A refactometer is usually a stable instrument if it is properly calibrated.

I'm using a swing arm gauge.