So what do you plan to do with them? They are going to need a much larger tank than that 55 within 6 months to a year At the absolute max depending on what size they are currently. You're going to have to do water changes at minimum of every other day and eventually they will be so big that they will look like a German shepherd in a dog crate. I'm Sorry if this comes off as a lecture, but the myth that fish only grow to the size of their tank is completely false and you need to have a plan in place before they get to that size.
Not sure, but they are not growing very fast right now so I'll upgrade accordingly for now and keep the water as clean as possible.