Magnesium and calcium levels

[Aquattro]

Everyone isn't dosing, only those that are and post about it. Unless you have a lot of coral using Ca for building skeletal tissue, you won't use it. If you want to use more, buy more stony coral
LPS use a bit, but grow slow. Softies use a tiny amount, nothing you'd notice. Anemones, nada.

[Metrontech]

So then do I need weekly water changes?

Is there a pro and con to not doing them?

I mean if my levels are food why bother?

[Aquattro]

Yes. Water changes replenish elements you don't test for and dilute the build up of nutrients. Reefing isn't just about Ca and Mg. 20% biweekly will likely cover all your needs, and you save a whack of cash not having to dose. Consider yourself fortunate!