Salifert.... Recently purchased. But have a new one coming with the bio brick to make sure it's not the test.

How long have you been using Aquaforest or zeovit or other additives.
I've heard of tanks having bleaching problems after prolonged usage of zeovit.
Do you dose phytoplankton

May or may not be related ...
I check my refractometer calibration every once in awhile. Found it to be off by 2 points last week. I was testing my water @ 1.026 but with a re-cal I found my water to be 1.028

Funny u mention this ...refractometer calibrated (Red Sea calibration fluid) and reading 1.024 on my tank... a Buddy checked my water with his tests etc his refractometer (calibrated with the same product... Different bottle) came back with 1.019!! What would allow a refractometer to calibrate correctly but read so far off? Can't believe I lost $6-700 worth of SPS to something basic like salinity :redface::redface::redface:

Could be the refractometer, I use 2 refractometer on my tank to test water, if one looks off I use the other one. Did you accidently drop your refractometer?
That could cause the discreptancy. Try adding salt water to your system instead of top off water to raise it slowly. Your colonies are probably under lots of stress so you don't want to shock them even more. How are the other corals and fish doing?

What salt are you using?

I also keep my salinity at 1.026 as this gives me a buffer of .02 either way which is always what my refractometer ago off on but usually 2 points higher so if it reads 1.026 it's sometimes 1.024. Don't thing I've ever heard a refractometer being that far off. Also measuring water when it's warm can give you a different reading than room temp but not by much.

If the hinge is getting sticky, the cover will not sit on the lens correctly. I have found that will throw the readings off by quite a lot