Six Line problem

You could try a trap to catch it. Some LFS will rent one out, mine does for $2 a day. Unfortunately the only other way is to tear down the entire tank. No way your going to catch him with a net trying to move around rocks. They are definately aggressive little buggers.

I used a trap to catch mine. I managed to nuy one second hand from Fleebay. The sixline and my chromis were the only ones to go in it.

Here's the link to my thread showing the sixline in the trap!

Good luck!

When I had to catch my sixline I just put an aquarium net in the tank with some food in it, after a little while the sixline got used to the net and swam in after the food. I leaned the net up against the front glass so there was a gap between the glass and the net, that way I could trap him in the net against the glass. Takes a little while, and a bit of patience but it works. Even if you miss they will come back for the food eventually.