Hi Fishlore, i have a 20 gallon tall tank with 6 pristella tetras im using a corner filter right now. Im planning to get a new filter coz i will move my filter to my 5G unfiltered betta tank. Im pretty tight on budget so im eyeing for a internal power filter or overhead filter for my 20G. Which is the better type of filter and what is the minimum gph i need? Thanks guys!