Not trying to hijack this thread but how do you use the epsom salt? Do you just put a small amount in the sump to dissolve or what? Thanks Mix the epsom salt in a cup of RO/DI or tank water, then add to sump or tank. Only about 1 tablespoon of epsom salt will easily dissolve in a cup of RO/DI water with some stirring. Adding about 10 tablespoons of epsom salt dissolved in water should increase your mag level up by about 100 ppm in a 150-160 gallon water system (figure 90 gal + partially filled 75 gal sump + 10 gal refugium = ~150 gal). Always test your parameters. Really? Wow, I'm learning quite a bit here. Now, do all of those need to be checked daily once they've reached their optimum levels? I test my Mag level every time after I check my Alk levels, maybe every 7-10 days. You may have to check more often depending on what works for you.