Advice- disease or just bleaching?

[Kluver]

Hi..I recently started converting over to SPS dominated tank. So far it's been around 3 months with great success. However, yesterday after water change I started to notice some bleaching on one of my SPS (I believe it's a milli--although I could be wrong). It has been doing great in my for a about 2 weeks until last night's water change. Everything else in the tank looks normal. I was wondering if it is an SPS disease or just plain bleaching? I'm running 2 kessil 150W along with 4 39W T5. I have been acclimating my LED without any ill effect so far. The one thing I did noticed was my sudden PH shift from 7.8 to 8.4 (due to water change and Kalk addition on ATO). I use ESV 2 part for my ALK and CA. My Tank info: the (--) indicate before water changes . Could it be a shift in PH causing stress or underling disease?
65 gal
ALK 11.2 (from 9.3)
Ca 450 (from 385)
Mg - 1320
NH3 - 0
Nitrite - 0
Phos - 0

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[pstank1]

Your alk increased by almost 2dkh from a water change? That could cause some problems. How quickly does your tank consume it?

 

[rps3]

I agree, alk is high IMO. Most run theirs around 8-9dkh

 

[M007]

Big swings in dKH can most certainly cause problems. Jumps in other perams should also be avoided!

 

[Kluver]

So it's the Alk and not so much the PH? I know that Alk and PH should have a direct relationship but surprisingly in my tank this has not been the case. My ph stayed at 7.8 despite my Alk staying at 9.2. I started to add Kalk to my top off and that has increased my PH but sadly so has my Alk. I guess I can stop the Kalk in the top off. My tank has been consuming Alk and Ca alot since I have not reach steady state yet because I have been adding SPS to my tank every week or so. Hopefully I will slow down and let the tank stabilized before adding more SPS. So what you see there is nothing more than stress to the coral and not some SPS diease?

 

[Kluver]

Oh I forgot..will it recover or is that dead tissue? If dead then I can just break those pieces off the coral than. Is that ok to do?

 

[cediss]

I agree with the others about avoiding large swings in parameters, especially the Alk. I have had corals, especially montiporas, but all SPS, fade with too rapid Alk shifts in either direction.

In you pics, the bleaching looks focal to certain branches and it would appear there may be some algae already growing on the skeleton. So from the pics it looks like tissue loss not bleaching. I don't see bite marks but I'd inspect closely for AEFW.