[N9CQB]

I've had a 90 gal reef with some red & purple mushrooms about 1/2 to 2/3 toward the bottom of the tank. The tank is 48 x 24 inches deep. Have other softies that are not affected like toadstool, hairly mushroom, kenya tree, xenia, leathers. H2O is RO only. Paramaters are Salinity 1.024, CA 400, DkH 7, Nitrates, Nitrites, Ammonia are 0, PH swings from 7.8 in am to 8.2 at night. Water changes are done at 5 gal weekly.
Used to have 260w PC + 80w flourescent, but now have 260 x 2 PC fixtures for 520w PC.
Over the last 2 months 3 shrooms have turned white with more looking that way.
There is also some white stuff all over the LR which does not come off.i.e doesn't look like precipitated CA. looks like die off coralline.
Ideas as to cause anyone ???