Lack of nitrates can absolutely kill corals. The first thing I did when I got into the hobby was bleach out a couple hammers and killed a colony of zoanthids from lack of nutrients. ULN systems can work and be quite stunning but I feel it's safer to keep some detectable levels of nutrients especially if you're not just straight sps. Corals need N and P to survive, especially LPS and softies.i would not increase feeding because it could spike it to get worse, in the past i had that issue and what i said above solved the issue. i never ever heard of nitrate being low being a issue, listen i had a 55gallon with 1 clown and 1 yellow tang with full of zoas and sps and i never ever had issue feeding low ,i kept my feeding minimal and do not shut off your skimmer... thats the last thing you want to do. shut the light off for 3 days cut the feeding for 3 days and do a water change on the 3rd day as well . see how that works.
Black box LEDs are great, no doubt there are better lights out there but they grow coral just fine.They are black box LED. I know, not great but it was what I could afford for the size of my tank.
They are full spectrum but blacked out the green and red spectrum when I originally thought this bacteria was algae.