Hi. I think for food you can feed them whatever you like. Flakes etc. or any of the other common food types. I think what other people are going to say when they read your post is that a 55 gallon tank is way too small for even 1 Bala Shark. I would imagine that they are still small in size now, but as far as i know they get very big as adults. 15" or so from what i have read. If/when they get that big, they won't even be able to turn around in that size tank. In the future you may have to return some, or give them away, or get a bigger tank. So as long as you're aware of this then until that time comes i would just feed them whatever food you have/like.