Chalice care

[A.ocellaris]

Hey,

 

Any advice on chalices? I got one a few months ago and lost it's beauty. It's still alive, but color is almost gone and I am not sure if it's too much light, or too less (around 120 PAR). I have low nutrients: Phosphate .03 ( hanna phosphorous, Nitrates 1-2, sometimes below 1 (Salifert) and I can't quite figure out what happened. There are other chalices that are looking great.

 

I recently started adding 4ml of Reef Energy (RedSea), to deal with the low nutrients, but not sure how long it will take to recover (if nutrients were the issue).