Struggling with Mg

[ahl]

Hello folks. Trying to stabilize my tank big 4. The one that misbehaves often is Mg.
I did a 20% WC 5 days ago and it measured 1320 a few hours after. I ran tests today and it measured 1230. That quite a drop for 5 days I think.
Others are at the same levels as they were after the WC
PO4 - 0.1
NO3 - 10
ALK - 7.4
Ca - 380

Api test kits for NO3 and seachem for the rest.

Salt is Instant ocean.

Thabks in advance for your help.

 

[ahl]

I just realized I didn't ask a question. Is this drop normal for a tank with a handful of sps frags? Nothing too big yet.
Also how you keep up with it? I've used BRS 2 part Mg to bring it up but it comes back down.

 

[W1ngz]

What is the Mg of your new water when you mix it? Mg drops aren’t really normal

 

[rushbattle]

This looks like measurement error. It’s unlikely to be dropping like that in your scenario.

 

[KrisReef]

My mg is impacted by salt levels, additions, and water changes. Consumption by reef animals is very low, it would not drop like your measurements have normally.

 

[johnalicia]

is there a lot of coralline in the tank?

 

[johnalicia]

how old is the tank?