What is wrong

[Parnold]

The problem - I am losing corals slowly but surely. I have lost 3 different montys a procilapora, blue tip stag, horn coral, and green digitata. They all seem to bleach out. I have a colt coral that turned dark purple and none of his polyps are out, not sure if he is dying. Other corals that seem to be fine are favia, bubble, frogspawn, xenia, zoos, and duncans. None of the corals were large, mostly frags.The fish all seem to do fine but my rose bubble tip has shriveled up and disappeared.

Water Parameters:
PH 8.0
Nitate 10
Nitrite 0.1
Ammonia 0
Alkalinity 100
Calcium 440
Phosphate 0.25
Magnesium 1220
Salinity 1.0245
Temp 78-81

I am using RO/DI for my top up and regular water changes, not dosing anything. Using an eco plus 633 skimmer and a phosban reactor.
Have two double ended 400 watt 14000K metal halides set 8 inches off surface for 7 hrs a day.
Circulation is 10 times through sump plus 22 times in display.
Cant seem to grow macros in the sump chaeto doesn't die but doesn't grow either, I used miracle mud at initial setup.
The tank is over a year old.
Does anything stand out that could be the cause.