Unhappy hammer - suggestions?

[lmm1967]

Have a hammer we've had since last September. Was a single head - has split to 3 heads within the past 45 days.

About 5 days ago is started opening less and less each day - now it's completely withdrawn but I can still see healthy tissue.

Newly added Duncan and plate tentacle corals are doing fine.

Water seems to be OK

35 salinity
Temp steady between 78 - 79
PH steady at 8.55 - 8.6
no Ammonia
no Nitrites
Nitrates & Phosphates are high but remain steady (60 & .36)
Cal steady and over 450
Mag steady and over 1400
Alk had dropped to 5 (YIKES) but I brought it up slowly over the course of 4 days to 8

All test kits are Red Sea and not expired.

I searched for pests and can't find any - any thoughts? Pics below so I can use tapatalk.

 

[lmm1967]

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[kevin21]

Without a doubt the high nitrates/phosphates as well as the drop in ALK is the issue. I would do weekly water changes and make sure you keep alk, ca, and mag as consistent as possible. Target levels vary, but for the most part in order to keep LPS happy, you need to be at:

ALK-8-10
mag-1300-1500
CA-400-500