My friend has a very cool tank. Well actually the tank is one of those water dispensers that have those big Corpell bottles on top. He cut open the top and made a lid, and put large pebbles inside, which wouldn't actually go through the dispenser but had enough spaces for the water to flow through in between. There were two tall fake plants, and one of those floating betta logs. Whenever he would need to do a water change, all he would do is press the tab for water to come out and add new water through the lid on top. I don't know how many gallons exactly, but that's a cool and smart way for water changes! Although there isn't a filter, i guess frequent water changes aren't a problem if its that easy!