Please help Lion fish stopped eating

[Dra49ers]

I have a lion fish about 7-8 inches, I've had him about 8 months now he was always hungry. I was feeding him 3x a week, rods predator mix, silversides, white shrimp from frys (rinsed of of course with ro) and monthly treat of ghost shrimp. Well about 2 weeks ago he was not interested an any food including ghost shrimp which he usually went crazy for damn near eating them as soon as they would hit the water. Also he seems unbalanced and being knocked back by power heads and sitting at a 45 degree angle. Sometimes he acts like he is hungry looking up food food when I am feeding but makes no attempt to eat anything. The only thing that has changed is that a month and a half ago noticed high nitrates 80ppm and started using Red Sea no3 po4. About 3 weeks later I lost a valentini (about a year old), harlequin tusk (7 months old), and blue throat trigger (about 6 months old). The trigger and tusk stopped eating and would hide for 2 days then would die on the 3rd day. Also I've noticed a cobweb substance on the under side of some of the live rock that appears to have started after the no3po4. The tank is a 180 gallon with a 20 gallon dump (bio balls), UV sterilizer, and bubble magus curve 7 skimmer. Not sure if these things are related but would really like to get my lion eating before I loose him, any suggestions would be appreciated. Sorry for the long post but figured the more info the better.