And it's funny you say thos. I had 3 hydra 26s on my tank, with 2 t5 bulbs retrofitted into my tank, all my acros always looked like crap. Browned or slowly died or just did nothing. I removed the t5s and 1 of my 26s and added 2 52. So now I have 2 52 and 2 26s behind them. I have them set at 65% and get more even coverage. It's weird bc its definitly more par than the t5s were putting out. So who knows.
I feel like 2 things you said stand out, and 1 thing you didn't say...
1x a month water change of a decent volume. May be causing too much of a nutrient swing, try more often less amount.
Your p04 is pretty low. (Agsin this is all opinion so take it for what its worth) I've found d better colors when my po4 as above .05 but below .15
And I didn't see a nitrate reading... maybe I missed it but you may just be starving your corals out. With now nitrates and phosphates
So that's what I noticed in your post that may help, you may not have enough spread on your lights. Meaning high and low par spots could be an issue as well. (Just a thought)
It took me almost a year to get everything dialed in and alot of trial and error. and alot of waiting to see if the change I made helped or not.