Hi LotzaOscars,
Well, I recommend you go to a fish store and open some filter boxes and take a look at the "mechanics" of these sponge filters or "corner" filters. basically you will need an air pump. You stick the airstone of the airpump underneath a layer of filtering material and allow a path for the air bubles back up while at the same time having some pores open in container to suck in water through the bottom sides....if you want to make a "powerfull" filter, you will need soem kind of pump to pump water back up into the ttank. This way you can construct an over the side filter taking water down to perhaps a big bioballs container and othe filter media after wihich it would be pumped up again by a pump. You probably don't want to build your own water pump also

, containers you can make out of acrylic glass, and they have the solution that melts it so you can bind it. You can buy this kidn of stuff in 'sign' making shops etc....Epoxy and silicone are also usefull to have. To tell you the truth though, you should get job

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Joe
www.cichlidfish.com