I have a 6-8 inch Niger in with a 8-10 inch Humu... and things seem fine so far. I also have a 125 gallon tank, so they aren't exactly on top of each other. I don't think a 55 is going to be big enough. Even as they are small, they creat a pretty big mess when they eat, and in such a small tank it may be hard to control your levels. GrouperHead even mentioned I might have too much of a load on my tank, and I only have 2 other big fish in that. ( and a few little ones). You may want to see what kind of filtration you are going to be putting on there first. Also, if you don't end up getting a bigger tank, it would SUCK to have to let your babies go. ..... my 2 cents