Refractometer calibration and Salinity Adjustments

[Patrick Cox]

I just bought some calibration fluid for my refractometer and I discovered that my salinity is lower than I thought. When I adjust the refractometer to the solution at 35 ppt, and then test my aquarium water, the salinity tests at 1.023 - 1.024. Kind of in between those lines I think. I was getting measurements from 1.025-1.026 (in the middle as well.)

So first questions, the fluid says it is 35 ppt at 77 degrees. My house is kept at about 68 degrees so I am not sure if this matters or not. If so, how can I make adjustments for this?

2nd question, assuming my water is actually 1.023/1.024, what is the best way to start raising my salinity? Should I add some salt to my top off water? Do water changes with higher salinity water? Other?

Last questions, if this lower salinity is correct, could this be having a negative effect on my SPS corals? I have been experiencing some tissue loss on a few corals and also a generally pale appearance. I have been battling with low nutrients but maybe the salinity has been a problem as well?

Thanks for your help!

 

[downbeach]

I would let your sample adjust to the temp by letting it sit for about 30 seconds before taking a reading.

http://reefkeeping.com/issues/2006-12/rhf/#6

I would use your make up water as top off, instead of plain RO/DI water, until your salinity is where you want it. This may take a little time, but that would be a good thing.

 

[mr.maroonsalty]

Just let evaporation bring it up by topping off with a wee bit high ppt make up water. IMO your lower sg shouldn't cause tissue loss; Id look at nutrients and flow dynamics.

 

[Epicreefer]

The main problem with low salinity is your Ca and Mg readings are going to be low by about 5%, alk is easily adjustable but it takes a lot of sups for the other two. But if corals are happy then it really isn't an issue. On smaller systems I would just top off with salt water instead of di, on very large systems I have added salt directly to the sump near the overflow area without issues but this was a large sump with little chance of salt crystals moving to the display area.

 

[hedgedrew]

Yes it makes a difference. I just had this issue. Both you temp on refrac surface and the calib solution temp makes a difference. Too cold it reads too low and youll have salinity too high in your display

 

[jerpa]

If your refractometer has ATC (automatic temperature compensation) then you don't need to adjust for temperature.