I am certain its from feeding and not rinsing my frozen mysis. I use PEMYSIS which has oils on it. I can see it when the frozen item touches the water. Plus I do feed my guys quite a bit especially my brittle stars and my snowflake eel. Also i randomly add live rock. Sometimes cured, sometimes uncured.
This might sound funny. However I find it so very fascinating how my CUC comes alive when I start to clean the tank myself. Suddenly I have crabs, stars, snails and all sorts of guys coming out of the woodwork cleaning, moving, just working themselves to death when they see me cleaning. Its sorta refreshing, sort of "Awe that's sweet" kinda thing lol. Like they are trying to help me.