I have a 90 gal. 17 month old reef tank with a sump and refugium. I have mostly softies, a clam and an anemone. once a month after the water change I test for ph, ammonia, nitrate, phosphate,calcium alk, and salinity. In my fuge I have a dsb, live rock and 4 mangrove plants. I just read somewhere that mangroves suck up alot of magnesium. I have never tested for magnesium. Infact, I can't even find a magnesium test kit anywhere in my area. so before I order one online, my question is, do I really need a magnesium test kit? or do my monthly water changes replace the magnesium that my mangroves use up?