What lights are your sun corals under and were they open before you fed them or after you fed them?
Me culpa, comparing apples and oranges, without mentioning this.
110W PC over 90g tank, was the same at 220W (the light is low intentionally, have deepwater fish).
Here is under 220W, top 1/3 of the tank, plus direct sunlight from the small basement window at the left:
The sun coral opens 3 times daily, within 15" after feeding fish, to pick up the floating pieces, a lot of them. The feeding or sun corals is done after evening opening, 1 hr before the vacuuming bottom, trying to keep 2x a week, but in a hot weather without chiller or air conditioning there, have to limit to 1x a week temporarily.
Sorry about your loss, Qckwzrd. Mine stands NO3 up to 80 ppm and PO4 up to 1 ppm (usually 0.5 ppm and less). What is disapproved - red slime and acoel worms in refugium, they produce something, that can be removed by carbon. Had to disconnect refugiums.
With some of babies: