i have 2 internal filters in my 36inchx15x15 tank fluval4 and eheimpowerball both sponge type media i have 2 tigers in it about3-3.5 inches i know i am going to need a bigger set up very shortly the filters are keeping the water testing ok but there is soup of crap on the bottom of the tank im hoovering it up every 2 days its a ball ache as i have sand in it if i get an fx5 installed will this deal with the bottom mess or not? can someone breifly explain how an external filter works ive become an oscar junkiee and want to get it right cheers!

most internal filters contains sponge and maybe a little bit of ceramic biological media. The water passes through these filters and the mechanical filtration will catch debris. Because they are very small filters with not a lot of mechanical filtration, they are just not up to dealing with messy fish like Oscars so you will be cleaning them more than once a week if you've got a sizeable fish.

external canister filters normally have various trays that the media sits in. because of the size of these filters, you are able to put a lot more filtration inside. The fact that the filters are so much bigger means that they can deal more efficiently with the waste, not only ammonia and nitrite, but also crap and uneaten food. If you use a suitable canister filter, they don't need cleaning for a few weeks so you only have to do worry about water changes.

you will definitely need a much larger tank ASAP, it's no wonder you are having problems with Crap in the bottom of the tank. Just getting new filtration is merely and help your situation. You may well be able to deal with the ammonia and nitrite, but the bigger the Oscars get, the quicker the nitrate levels are going to rise and you'll find yourself doing two or three water changes a week. Even then, you still may have water quality problems

External filters work the same as internal filters, they are just bigger and they dont go in the tank (they are connected to the tank by pipes). They are much more efficient than internal filters