sack

I care for a Saltwater tank at work and I am learning as I go. We have a Lawnmower Blenny, Foxface, Midas Blenny, tangs, clownfish, pajama cardinals, cleaner shrimp, snails, hermits, coral, etc... today I notice 2 new distinctions in the tank. Mind you Salinity is normal and Nitrate/Nitrite test...