Just that if all participants had enough feeling of safe territory (and that's kind of hard-wired into them, regardless of the size they are yet) they'd be easier with each other. There's just one trick I can think of, which is to try to barrier-off a third of the tank for the clown (assuming he's at a far end) and put up a vertical barrier, a spire of rock, something that forms a 'border' that separates the clown and the tang in terms of territory...if that doesn't work, the clown, as the fiercest damsel you've got, and that tang, are going to continue until somebody gets seriously hurt, and it's likely to be the clown, once the tang gets his measure. If you can give 2/3 of the tank to the tang by that method (clowns are generally content with a little less territory, unless they've got the notion they own it all...) You could also try withdrawing the clown AND the tang for a cooldown period, and starting them both again---but that's likely more hassle than you want to get into. Try to 'fold space' by rock arrangement and see if that works.