Thanks guys.
Yes those black thing. Look like it's poop, and when it does that the whole anemone will shrink. Seems like it uses alot strength to pass waste out . hehe
Had similar issues too and gotten the snails to solve my issue. Amazed by their cleaning . haha.
Does your sandbed has brown algae too? I am seeing slow growth but still trying to find a way to retain the white sandbed.