Dosing - can't find the right levels.

[ScubaSteve]

I can't really offer a solution to the Mg problem other than you didn't wait long enough on the tests. Let the tests sit for 5 mins before you determine what the reading is.

Alk can be a bitch. I found my tank actually DOES use a ton of alk when given the opportunity. So don't be surprised if you do end up using a lot here, especially after an upgrade. This is also because water actually has a fairly limited solubility of carbonate compared to calcium, so alk fluctuates more than calc.