There are several dozen, maybe more, ions that can get out of balance in artificial reef systems, we only test for a handful of them and even then with test kits that would not pass muster in any real lab in the country. It's why dosing may not be the total answer. Water exchanges is a pretty bulletproof way of maintaining that ionic balance, especially for things like potassium and other necessary elements we don't test for. Maybe that's part of the mystery when we see posts about my corals dying and all water parameters are spot on. Maybe the parameters you are testing are good, what about those you don't test for? I don't do large water exchanges, just smaller ones every other week. I am rethinking that.