Help: Some of my test results are worrying

[newreefer_59]

Have a 150 gallon reef tank up and running for one year to this point. Some LPS and SPS coral and 5 fish, some cleaner shrimp and snails/crabs. I do a 15% water change EVERY 10 days. My last tests a day after the last W/C (yesterday) were:

Calcium ~350
Magnesium ~1200
KH ~ 6
PH ~ 8.7

All other tests looked fine. The tank and critters all look fine too, except my small clove polyp softie all died after it has been there for about 6 months.

I have been dosing Calcium, Magnesium and KH from those Coralife store bought bottles......Is there something I can do to bring these levels back.

Please advise......much appreciated!