So for the fish only QT, alk/ca/mg is irrelevant? I was reading where it was stated that alk needed to be maintained in order to not have PH issues?Simple. I never check them.
If it is just a small QT tank for corals, just do a water change now and again. SPS grow great and I never check them. We are talking about a QT tank which is probably a nano. People run nano's on just water changes... should be easy for inverts and frags. If it is a full blown SPS tank with colonies, that is one thing... but it's just a frag QT tank. You don't need to dose 2 part for it.
I don't even check Mg and Ca on my big tank. Just alk since 2 part is dosed off that anyways and the 2 part also adds some Mg so between that and water changes it never changes. I realized I was testing Mg and Ca for years and they never were out of range so I stopped that BS.
Fish don't care about your alk/ca/mg so don't bother to check the fish one at all. Nothing should be using it up anyways.