For my 10 gallon fry tank I use a air-driven corner filter. They are surprisingly efficient and I just change the floss whenever it gets dirty. They don't suck up the fry, there is no heavy current, and with the surface agitation, it causes the water to be well aerated. If I have to use as a hospital tank, there is no carbon it it to worry about. It is a great all-purpose arrangement. I keep they fry in a breeder net on the opposite end to ensure they get fed. When they get bigger they are taken out of net and left in the 10 to grow to a large enough size to sell/rehome.