I know this is a long read but I think you might want to read it because your salinity may not be what you think it is.
I just want to let everyone know what I have been going through in regards to Salinity. Keeping your salinity stable and around 1.025 to 1.026 in a reef is very important
I had a Vertex Refractometer for about 5 years and I have been using Pinpoint Salinity Calibration Solution that is about a year and a half to 2 years old to calibrate it. Before that I was using RO water to calibrate it. I have been getting funny readings lately, sometimes it was high sometimes it was low and I had to re-calibrate the meter after each test. I also found it difficult to read. So I decided to buy a Pro-1 refractometer (one of the best) and some new Calibration solution. I purchased the Sybon Standard Seawater saline supposed to be calibrated to 1.026 or 35 ppt. Upon getting home from J&L's I tested the new refractometer that was supposed to be pre-calibrated when I bought it. I immediately had to re-calibrate the new refractometer. Seemed odd. When I tested my tank water my salinity was 1.031 (41ppt) Ouch!
. I tested my original Pinpoint calibration solution and it was 41ppt as well.
At this point I panicked. The next day I went in to J&L and took both my calibration solutions and asked them to check them. They really weren't too much help he said the Pinpoint was a little high and the Sybon was a little low. He told me they hadn't calibrated their refractometer lately so it was likely off. He said that the Sybon is actually calibrated to natural sea water not reef tank water it usually measures a little low. They were very busy last Saturday. So I went back home and checked on the web and they say there is a difference between natural seawater that is 1.026 and mixed tank water that is 1.026. Also that the Pinpoint is a better calibration solution for reef tanks and that the Sybon is for checking the ocean.
I purchased a new batch of Pinpoint calibration solution and I had to immediately recalibrate my new refractometer back down to the original settings. The Sybon calibration solution measures at about 1.0235 instead of the 1.026 the solution says it is. Anyway my tank was still up around 1.030 and I have been slowly lowering it over the last week to get it back down to 1.026.
The moral of the story is do not trust your calibration solution especially if it is old because the concentration does change over time. I never left the calibration solution open nor did I ever contaminate the solution. Who knows how long my salinity has been high. It does help explain why my calcium, magnesium and Potassium levels have been high.