What would cause my salinity to raise?

An 11% evaporation rate would mean your salinity would go up by 11%. So unless my math is wrong, your salt would go from 1.023 to 1.136, which is "off the charts" for all intents and purposes for our inhabitants.

Think of it this way--if you have a 90 gallon tank, if 11% of your water would evaporate, that's 9.9 gallons! Not only would your water level go down at least 2 inches or so, but your water would be super hyper-salinated to the point where you might lose everything in your tank.

Here's an article that's sort of related to your question, and will give you an idea about evaporation rates, dilution rates, and their respective effects on salinity. I think the author really knows what he's talking about!

 

I'm glad we're discussing this. It's an interesting subject.

To clarify, the hydrometer measures specific gravity, not salinity. They're not the same.

My research found that the mathematical relationship between specific gravity and salt concentration are not 1:1. At 74F a 1.023 sg corresponds to salt concentration of 31.9ppt. And 1.026sg corresponds to 35.9ppt.*

* Algone.com - Saltwater salinity and specific gravity in aquariums

Thus, an increase in specific gravity from 1.023 to 1.026 would be a 3% increase. But -- the corresponding increase in salt concentration from 31.9 ppt to 35.9 ppt would be a 13% increase. Clearly not 1:1. So, as I change the salt concentration in a tank (by evapporation) I'll not see a 1:1 change in my specific gravity.

In other words, as my water level evaporates by 3%, I won't see a 3% change in my hydrometer reading.

Second, what I calculated makes sense to me in actual practice. If I lose 3% to evaporation, my sg doesn't increase from 1.023 to 1.026. It probably goes up to about 1.024 maybe. I'd need to lose more than 3% in evaporation to see that kind of change in specific gravity, in my experience.

 

Like i said my refractometer needed to be recalibrated. My sg was not 1.026 it was 1.024

 

that makes sense. we're just chatting about how much of a change in evaporation would be required to see the kind of change that you thought you had before you recalibrated.

 

when u recalibrate the refractometer use pinpoint salinity calibration fluid. I let the solution sit in zip lock back floating in the aquarium so the solution is at about 78 degrees. Says it accurate +-1 at 77 degrees, so ive found acclimating the solution makes the reading more accurate.

 

we broke one, thankfully it wasn't in the tank, but it was on the floor, happened months ago and yet i still find myself stepping on those little black ball thingies on occasion :-/