I think one of the biggest issues is that some people dont realize that Mg is a key ingredient for Alk and Calc to function in a reef tank. I have noticed that mine fluctuates around 1300-1450 at times. If you are chasing numbers and have huge inconsistencies, check your Mg. I could almost bet its the culprit in providing a large array of inconsistent reading and poor coral health. You can buy Mg supplements but most ppl use Epson Salt. I have never used epson salt for two reasons, one, Mg supplement is fairly inexpensive and two, the epson salt (from what i have read) can cause a sulfate build up that is normally unwanted in reef tanks. Hope this helps. Read up on Mg. You will be surprised of how important it is it the Alk and Calc make up.