Funny this came up. I was at petco today to grab some snails and they had a little yellow tang and a bigger scopas together in a ten gallon.. maybe 20gallon. But the scopas was beating the heck out of the yellow. I told the guy he should separate them at least. He said he would but he also claimed he has had tangs together in that same tank and they got along fine. Ultimately not my call just voiced my opinion bought my snails and went home.