its a blue spot tang as i have on also,this tang is very sensitive to temprature so i could be your water is getting to cold over night also these tangs grow massive. try garlic on his nor weed failing that take him out as the others said.there is a picture of my blue spot tang on here in marine photos just to make sure it is the same type of fish
i am gutted now i brought a blue spot tang and a wolf eel 12 months ago,at the time the eel was about 6inches long and the tang was about 3inches long since then they have both grown massively the eel is now a foot long and the tang is about 7 inches my tank is 4 foot x 2foot x 2foot 75 gallon ish. i know they will have to go but i love them so much. all i want to say to all of you is please think about what your buying when go to the lfs to buy your lovely fish.not only will is it unfair on the fish to be in a small enviroment but it breaks your heart knowing you will have to move them on to another home also does anyone know if after fish spawn they stop eatting or lose there sight as my eel spawned a month ago and now seems to be blind.
at the moment i have a mix of differant corals but some are growing into other corals areas i know that corals attack eachother and can kill eachother off but do all corals do this? if so i will have to arrange all my tank which will be a nightmare with the aquascape i have.and i have a toadstool attached to a large piece of lava rock which i want to get rid of how can i seperate them?