I've got some green star polyps that are encroaching on the base of a large colt coral. Do I need to trim them back, or will the colt hold it's own against them?
I would kill the star polyps that are encroaching. Maybe try kalk paste. Just be careful with it as it will injure whatever it hits. Make sure you turn all the flow off in the tank, and let the paste sit on the polyps for 20 minutes.
Cut them off and trade them. People want these things as unpopular as they seem in the posts. Just keep them seg'ed off and you'll be fine. Of course you will have to trim back at some point of course as your post points out, but hey anything you don't already have is usually cool right? Mounted you can usually trade for some nice food from an lfs
Is there anything I can put as a buffer that will stand up to them? They seem to spread about 1"-2" per month. It's only a 30 gallon tank, so that's a lot of realestate. I don't look forward to having to kill or trim them on a monthly basis.
Put rubble up against them. When they grow on to the rubble, tear the encrusted rubble off, and replace it with new rubble. Trade in the frags, give 'em away, sell 'em... whatever you like.
I doubt they will kill or grow over a colt, but you're better off keeping them pruned and under control.