montipora color fade

[scubacane]

I have JBJ 28 gallon 186 watt metal halide- 2.5 years old- multiple SPS- montiporas, acroporas multiple LPS- torch, frogspawn, a sinularia, open brain, tongue coral, one clown- parameters- nitrate 0, phosphate 0, calcium 440, alk has been trending down- 7-8 lately, temp 79 F, SG 1.025, weekly 4 gallon water changes with distilled bottle water . Lately my large orange montipora, which sits about 5 inches below surface and has grown 10 x its original size in 2 years, growing up the side of the tank, has started to have a diffuse color loss, not a total bleach. A montipora on the other side looks fine. I havent added anything new to the tank in quite some time . My sps corals have seem to coexist fairly well with my lps .I I have decided to start another tank to separate my sps and lps. Possible causes-1. a sinularia that has lived 2 inches from the montipora has grown out of control - I pruned it while it was still in tank 2 weeks ago. Could it have released a toxin that caused the bleach? Since then I have learned that sinularia and sps dont mixed well however it hasnt been an issue before.
2. I cleaned the glass and acrylic covering for my lighting really well of salt and grime several weeks ago. Could this have affected the light intensity to a degree that would cause a bleach?
3.I tweaked one of my outflows so there is a bit less shimmering of light on the surface ( again ? affecting intensity)
I am getting my alk up, changed back the outlow. New tank wont be ready for a couple more weeks however I plan to move all my LPS corals and softies to this tank and leave my current as a SPS only tank. Of note as well, when I look at the montipora from above, the plates that are growing underneath have better color than the plates higher up making me think it is a light intensity issue

 

[BEEKER1]

Couple of questions:

Did you recently change the halide bulb? How old is the bulb?
When cleaning did you knock salt creep back into the tank?
Does the sinularia have sweepers?
What did you use when you cleaned the glass?
By changing the flow have you re-directed a flow pattern this coral was accustomed to and now it is getting blasted or not getting the flow it is used to?

 

[scubacane]

metal halide bulb is 4 months old
no salt creep was knocked in tank
it is possible that redirected flow happened however have since corrected
the sinularia doesnt send out sweepers has small polyps that have occasionally grazed side of montipora cap and bleached edge in past but nothing more significant than that

 

[scubacane]

I have enclosed two pics- one from about one month ago- monti is in back upper L corner and a closeup from today