low Ca/ high mag?

My magnesium has always been a little high (usually 1500-1520) but i tested it a little while ago and it is up to 1600. I understand that this isnt harmful, but i dont supplement mag so i dont see how it could be being added to the water. Also my calcium was down to 390. I have a basic understanding of the relationship between mag, ca, and alk, but im not sure if low calcium could cause a high mag reading, or vice versa? if not what else could cause my mag to get so high?
other params:
ph- 8.1 (salifert)
salinity- 1.025
alk- 10 dkh
alk, ca, and mag were tested with a red sea kit. TIA

 

Are you including the proper airgap in the tritration syringe?If not,you may just be getting a false mag reading.I think the red sea mag test is a good kit overall,but it is a touchy one,the syringe air gap is a pita.Just a thought.

 

Might be coming in with your water changes as well. If it's not being stripped from the water column it could start rising over time with repeated changes.