Brittle stars in reef?

You do not!!! Don't you know if there was a blue one out there, I'd have it! ;D

 

To put Triplemom's words into something more specific:

we have a Red Brittle Star, he's probably 1ft in diameter if we stretched him out. Maybe 8 inchs..8-12 inches. We call him the "Gorilla" because his arms are thick and have the likeness of a gorilla haha. We also have a harlequin serpent star, the "black and white" banded. He's actually brown and tan IMO, but he's been in there since week one. Fully grown about 4-6inches in diameter. Then we have a recently bought red serpent star, 4-6 inches. He's definitely not shy! He charged out at feeding time yesterday right out into the open. So naturally I had to stick my hand in there and give him a chunk of krill

I think they're fine. Yes, avoid Green Brittle stars. They look cool, but can be predatory. At least your fish would "pass on" in their sleep...I think...

 

Yep I have a large green brittle in my RT. It pretty much hangs out at the base of my LR and when the lights go out he moves around a bit. He eats whatever the rest of my livestock eat, but on the occasions that flakes go in, it really enjoys those! No probs with anything going missing yet, but only been 2 weeks. I have snails and crabs and a green star polyp, along with a maroon and Clarkii, damsels, and a Coral Beauty.