Will a GSP colony over grow apstasia?

[Delphinus]

Rule of thumb that works for me: if you paid good money for it, GSP will overgrow it and smother it to death. If it is a pest you ordinarily wouldn't like, GSP will become best friends with it and let it live. Well, maybe not, but it probably can't overgrow things like aiptasia. Since aiptasia is mobile, and has a reasonably strong will to live, the best case scenario is GSP grows over the spot but the anemone is long since moved to a different spot by that time. But the more likely outcome here for you is, since you probably paid good money for the GSP, the aiptasia will sting the GSP and the GSP will recede.

Literally the rule of thumb is that the more expensive coral will be the loser in any showdown.