Get your water tested by another sorce or LFS. You'd be suprised how many false tests happen.
Lighting and phospahtes are my guess, how long did you let the NP pellets run? I noticed a bit of brown algae about 2-3 weeks from starting them.
When were your bulbs last repaced/installed? Coral bleaching is due to lighting, low Iodine & Strontium
Another product I found that works for algae is PridiBio BioDigest,
http://perso.ovh.net/~prodibio/index...&eau_id=2&id=3
Ken - BWA