Coral STN

[Fishyfish22]

I'm having STN issues with some of my coral, mainly two acro colonies are starting to slowly bleach from the base up: My HW and WD, I'm also noticing other colonies are slowly started to whiten on the bottom branches as well.

Tank is 300 gallons.
My levels currently are
alk: 9.9
Ca: 500
mg: 1330
No3: 5.2
PO4: 1.74

Lights are Radions, on the AB+ Spectrum but dialed down about 30%
observations:
for the last few weeks, my walt disney had been turning green and was losing the golden tones it had.
Normally it takes a day for film algae to cover the glass, currently it's been 3 days and the algae that normally covers the glass hasn't struck. can't believe I'm saying this but I kinda miss it
Chaeto isn't melting, but it's dying off and falling apart. What was a fuge full is now reduced to a few golf sized tufts of chaeto
my Welsos, which were previously inflated, are currently closed and unhappy.

I've been having issues with nitrates being up, I have a decently stocked tank with several tangs, large enough to keep nutrients up higher than 5.2
does anyone know what I should do, or what seems to be going on? I dosed 40mL Brightwell neonitro, what's the next step?

 

[Randy Holmes-Farley Verified Community Expert]

The phosphate is certainly excessively high if 1.74 ppm is not a typo, and I'd look to that as a possible concern.

have you ever dosed trace elements such as iron and manganese? That might help the chaeto.