High Stable Alk, Low Calicum, High Mag, why?

[chris.gries.50]

I tested my tank last night and my Alk was stable at 10.1 using a Hanna tester. This is normal for me and where I keep my Alk. My calcium was 330. It usually is around 375-400. My mag raised to 1520. It has been steadily increasing for a few months from 1300 to 1520 last night. I dose 3 part ATI essentials. I lowered my dosing of the 3rd component which contains the mag, but my mag. increased. ATI recommends dosing all three components equally. Nitrate and Phosphate are low, NO3 0, PO4 0, usually 5ppm and 0-.02 ppm for PO4. I use Salifert for calcium, mag and nitrate and Hanna testers for alk. and phosphate. I use Instant Ocean for saltwater. Tank looks great. SPS growing. It is an established tank, but I started a reboot about a year ago, after a loss of fish due to disease.

I have a few questions;
Possible reasons why, other than testing error/bad test kit
Should I adjust dosing? Should I lower alk and raise calcium dosing?
Should I level thinks the same and use another method to raise calcium?

 

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