Hang on back filter should be fine. It's like any other tank you have, the filter flow rate should be at least 6 times the volume of the tank. So if you have a 55 gallon tank, your filter(s) should have a flow rate of at least 330 gallons per hour. 6x is probably the lowest you should go, some people recommend much higher.
You should add some marine salt to the water as they get bigger. They should be kept with other brackish fish like monos and puffers after they get to be about 3-4 inches. Smaller than that, they can be kept in fresh water.