Struggling ORA Red Planet

I have a piece of ORA red planet that is losing its flesh at the tips.  I'm really not sure what's going on.  I've had the piece for 3 months, it started receeding 3 weeks ago.  I only have 2 acros in the tank, the red planet and a green slimer.  The slimer is doing excellent!

ph: 8
phosphates: Hanna checker says 0 but I am battling a bit of algae
Nitrates: 0 - 5 ppm
Ammonia: 0
Nitrites: 0
Alk: 9.2 dkh
Calcium: 430 ppm
Magnesium: 1400

I noticed the tips starting to receed three weeks ago when I was maintaining alk at 10.5 dkh.  I did some internet research(always conflicting) and thought it might be being caused by high alk so I slowly lowered it to 9.2.

Lighting is LEDs.  90 Gallon display with 30 gallon sump(refugium with chaeto).  Manually dosing BRS 2-part: alk in the mornings(about 25 ml) and calcium at night(about 20 ml).  Jebao wp40 on w1 s2(standing wave) and wp25 on else.  The coral is not directly hit by either powerhead.

Sorry Mark, no full tank shot or even a shot of the piece.   I'll get them up when I get home from work.

Thanks in advance for the help!  I'd really like to save this coral!

Two Three no four thoughts, in order of likelihood:
1 - downstream from a coral with stronger allelopathy?
Solution: Move one or the other coral ASAP
2 - change in lighting?
Answer: Reduce lighting or move coral deeper.
3 - coral is downstream from a patch of nuisance algae?
Solution: Get more herbivores to eat the algae. Physically place hermits and snails on the patch of algae. scrub the patch with a toothbrush(in the tank)
4 - other chemical change in the system like a bad chemical accidentally introduced or even a new supplement/additive?
Answer: Add/Change AC making sure water is flowing past the bag/pellets/granules and/or stop using that new additive.

IME, the reason for most nuisance algae problems is that the hobbyist has not maintained the population of herbivores(snails), has been overfeeding and has been doing water changes more frequent or larger than 10% monthly.

Alkalinity most likely is not nor never was the problem. 8-14 dKH is an acceptable range.
FYI, Alk and Ca supplements can be added within 30 seconds of each other so long as they are poured in to a dispersing current. It's not a big deal. If they are added too close together, a harmless "snow" forms and quickly disperses. Just wait a few seconds longer.

Aloha

You sure its not just new white growth tips? My red planet tips look bone white when growing.

What's your recommended GHA removal method?  The rock it is on is in the middle of the structure and would be hard/impossible to remove without major aquascape changes.

I don't have a pic(at work right now).  I am running GFO at 3/4 recommended usage in a fluidized reactor.  I have ~40 nessaurus(sp?) snails, ~18 astreas, 2 trochus, and ~20 hermits of mixed type.  Chaeto in the fuge doubles in size about every 6 weeks.

I haven't been very vigilant in cleaning detritus off of the bottom of the sump.  I'm planning to get rid of that this weekend and add sand to the fuge chamber and a few nessaurus snails as well.