From what i have heard there is only one color of brittle you need to worry about eating fish. not sure if its true or not but i beleive its the green and black ones.

I have had a sand sifter in my 34 g since the get go and hes fine. they may get big but im sure someone would love to trade a smaller one for a larger one. ialso have a pearly (yellow headed) jawfish. but digs until he finds a home he likes and then just home maintanence.