Sounds like what I had In my tank. I used phos remover media but don't leave it in for more then 48 hours or it will leach back into the water, other then that it seemed like my tank got better on it's own after a while I set the lights on a timer and it corrected its self because it didn't come back after i got halides. Try turning your lights off for 2-3 days. Your corals should be fine and the fish don't seem to mind. and ro/di will deff help. I use tap water and all my parameters are 0. But my tap water seems to be really well and that's all I have ever used in my salt water tanks but I have had ppl say it is better to use it there is less crap in it then tap water ie. ammonia, phosphates, ect
Hope it helps