Have had my gem for about 2 - 2 1/2 years. It’s about 4 1/2” and in a 450. 12 other tangs, including three zebrasomas. Neither the yellow nor the desjardini sailfin were a problem but the purple was. Came close to killing the gem before being removed for a month. Since reintroduction the gem and purple have tolerated each other. Occasional ripped fin, but that’s about it. Other tangs include Fowler’s, zebra, chevron, Hepatus, four different Naso. Some gems have a yellow tail, others a white one. I think it’s based on where they’re collected.