I second what shifty wrote. I can't use the bleachcalc because it's a Windows executable and I run a Mac. The Pool Calc is HTML based and runs on any platform. Like you, I use it for bleach and Borax calculations and occasionally for "effects of adding xyz". It has never lead me wrong but I now have enough experience with my particular pool to know when I should question any results obtained. The caveat I follow is "add half now, test, add more later".