Good for that. It's possible you have something in the tank that is dissolving and releasing calcium: old coral can do that, some crushed coral sands---I'd say the last thing you need is calcium additive, for sure! One of those salifert kits lasts half a year even used often, so that will help---hard to buy them all at once, but the most important are the alk and cal tests, plus your ph and salinity. [The others are just finesses, to be tested only when nothing else is making sense. For instance, you can spot excess phosphate just when algae grows: you got algae, you got phosphate, so no need for that test. Nitrate/ammonia---just hope you don't have any, so if your system has been clean under your general habit of husbandry, it should stay clean unless something dies and pollutes it.]