Corals dying

[Seriak]

I can't seem to figure this one out.

It started with some algae growth on my birds nest and setosa, then my monti started to bleach and get covered in green film algae, now my LPS are slowly losing their heads. A couple SPS colonies bleached over night and now some of my smaller SPS are starting to have algae form on the tips.

My Parameters are as follows.

Salinity 1.026
Ca 350
Mg 1250
Alk 9.0
PO4 0

I did introduce bio pellets around 2 month ago, but I went very slowly. I also started to dose CaCl2 around the this time. I have a new skimmer that I am running fairly wet and I have to empty it every couple of days. I don't have a nitrate test, but hope to get one soon.

I tested my water and it looks like my membrane needed to be changed as it was in the 16 range. I have now fixed that and its back down to zero. I will do a big water change tomorrow, but can anyone else think of what I might try.