Magnesium and PE

[Skimmerking]

I have been testing my tank out with tests kits and checking levels. Now last night i found a article on Reef Central about Magnesium and PE. I got me thinking about May be that is why the corals would doing better in my tank. I dont have a Mag test kit, and never tested for Mag. I'm thinking that maybe I should get one But i can't be bothered paying $40 for a kit that only has 40 tests to it.

But sides Testing what is the highest the MAg can go up to I hear that 1350 is about the average PPM. I thought about just adding a certain about every 2 weeks or get in the mode of doing it with my water change. But my water changes consist of 20 gal per month ... will that still be enough.