Nitrate Test
I'm going to assume you're getting zero ppm's on a nitrates test.
Based on what you described, it seems like you could feed more. Do you agree?
Additional Feeding
If you have more room to feed, do so. My feeling is to just try adding one more serving per day of any one of those food options you mentioned.
You may even have quite a bit more room to feed, but just a moderate change being the idea for now.
See if the additional fish byproducts (ammonium and urea being just a couple of them) are enough to make that coral happier.
If you haven't considered adding live food to your repertoire, now would be a fine time to start feeding blackworms or newly hatched brine shrimp, just to name two possibilities.
Liquid Nutrients
If you don't feel you have more room to feed, then consider KNO3 dosing or amino acids. I think KNO3 would be preferred.
I also wouldn't feel bad about letting PO4 get up as high as 0.50 ppm or so. There are liquid additives you can use as-needed here too if feeding more isn't an option.
2¢
