Additives are not necessarily "not natural". I don't advocate putting in any additives that you don't know your existing levels of, or just putting them in because someone said to. But additives to correct a deficiency is fine in my mind. Most of these additives, as far as calcium/alk
/mag/trace minerals are 100% natural, as far as ingredients. There's nothing unnatural about calcium chloride, epsom salts, etc.
If your calcium demand is high enough, and you want to keep a consistent calcium level, you'll have to dose calcium/alkalinity. You may not be at that point now, but if you keep adding corals or your coralline algae takes off like gangbusters, you'll need to do it in the future - assuming you want consistent calcium levels between water changes.
After reading Mr X's comment about adding straight calcium, I need to add a little disclaimer to my "... use TurboCalcium to raise your Ca
levels..." comment. Adding just straight calcium, which TurboCalcium is, will definitely lower your alkalinity. The two go hand in hand - you can't have higher calcium with high alkalinity. (Not that 420 calcium is "high".) But as you raise one, you'll lower the other. From my experience with IO, the little bump you're talking about in Ca
won't really lower the alkalinity *that* much. But for sure... when changing any parameters like that, have a test kit handy and make sure your alkalinity is still where you want it.
I haven't tried IO for a long time, but within the last year or so they've changed the formulation. The Ca
is higher now than it used to be. That might be why the higher numbers seem off to some that have used it in the past. Then again, I've also found the API calcium test to be really fussy. And I traced it to the same reason - how hard you push on the bottle and how big the drops are really skew the results. Salifert is much more reliable and consistent - less room for human errors.