Recently both my tangs seem to have lost some weight. i feed them 1/3 a sheet of nori every day and they also eat the flakes i feed the clowns and they pick at the algae all day. But recently they're skeletal structure is visible when the light hits them at the right angle. definitely no where near as bad as i've seen fish before. but skinnier then i'm comfortable with. i recently started soaking the nori in the amino acid supplements (hopefully that helps) and i'll start feeding 2/3 of a sheet i guess. 1/3 in the morning 1/3 at night especially since the idol really like the nori (it's 1 idol, a yellow tang, and a naso tang) I'm pretty sure they don't have any parasites.