Purple will be fine for more than a week in that refugium. Take as long as you need to make sure that Gem is comfortable and fat and happy.
In a 300 I think you would've been ok regardless, especially since the Gem is bigger than the Purple. But yeah if you want to do that just to be safe, go for it.
I have a 300 (8 foot long, 30 inches front to back. 24 inches high). I currently have 11 tangs in it Haha.
Wow!! Great yours all get along. When did you add that gem in that mix. I previosly tried a gem (about 4 inches) and my kole tang bullied it to death. I was finally able to rehome the kole (about 5-6 inches) - he was a jerk. My hippo (about 8 inches) can sometimes be a bit bossy too so hoping all goes well this time with the big gem. Pending the weather he is set to arrive Tuesday. Fingers crossed.
Purple not happy but put a clam in the refugium that he is happily going ti town on without the competition from the others. Glad to see him eating.