I have alkalinity and calcium test kits. When I bought the corals, I asked both stores what tests I should buy, and they both said as long as Im doing weekly water changes, I dont need to worry about the alk, calcium, magnesium, etc because the salt mix gives what they need, plus the waste from the fish, so I dont have any other tests. Those ones came in the API test kit I bought when I first started the tank, which almost unanimously people have said API tests suck, so I havent touched them since. I got ammonia, nitrite and nitrate tests from better brands for the tank but didnt buy any others for corals.