SPS Burnt/receding tips

[Herbie's Reef]

Recently some of the tips on my sps have begun to receed. Most notably on a few of my acros and my setosa. During this I have also noticed a reduction in growth tips on other corals such as my forest fire digi or BOP birds nest along with a lack of yellow show in by bbgum digis.

Current Params:
Alk: 9.9
Cal:470
Mag:1440
Nitrate: 8.9
Phosphate: 0.08
Salinity: 36ppt
Salt Mix: AF Reef salt - just swtiched to IO RC but have not mixed a batch for a water change yet
Dosing: 4.5L kalkwasser, 10ml AFR
Tank size: 85g DT, 40g Sump
W/C schedule: 15g weekly

I have also been battling prorocentrum dinos for multiple months now and have been consistently dosing 20ml of MB7 daily along with 10ml of Live PhytoFeast twice daily. I currently have been dosing silicates on and off but have bought much more so I can begin dosing silicates consistantly.
My Alk Cal and Mag are high for my liking due to a tank crash about a month ago causing all three to spike, after drastically lowering dosing they have all been stable around these numbers. I have been working on lowering salinity after I accidentally raised it too high from a point of 34.5ppt.

Thank you for your help, photos are linked below. The majority of these corals are in the lower portion of my reef and under high flow.

 

[Herbie's Reef]

Also I have never seen a fish nip at any coral. Just need some advice on what could be causing these burnt tips and recession? I think it may be the elevated elements but I’m not sure…

 

[dwest]

My acros get tips like that when I use GFO. Also, if you had a spike in alkalinity a month ago, corals might still be affected. I would keep things as stable as possible and cross my fingers.

 

[Lavey29]

The instability the past month you referenced is the reason your SPS are showing decline. As mentioned above keep things stable and cross fingers. You can always snip off a branch if it is failing so the problem might not spread to the entire coral. I have done this with success.