I'm Perplexed

[Lady J]

I've had my beautiful male for 1 week---he's been doing great, out swimming and exploring. Yesterday I added 6 corys and 5 rummy nose (sp?). My betta has gone after none of them which is great. What concerns me is the opposite: he now seems to be hiding at the top, behind the penguin fitration. If he does come out to swim, it's very brief and then he's hiding again. What's going on? Are they too boisterous for him?