funny you should post this.
I just watched as a shower of mini brittle star arms cascaded through my tank. I have a big powerhead on a timer, 30 minutes on, 30 minutes off, I guess one crawled in there while it was off.
But what I did was glued some screen (actually circles cut from a salvaged fluval filter basket)
inside and then glued the nozzles in place over it. Has worked great, reduced the flow just enough so it's not a whirlwind and keeps my important critters from getting in there. I was terrified my pair of cleaner shrimps were going to go in there if I didn't do something.