Sometimes it is difficult to seal the lid on canister filters and they can leak. If you ever have problems with getting the lid to seal you can use Vaseline on the O-ring to get a good seal. The sand filter flow rate must be adjusted so that you do not blow the sand into the aquarium. Many owners of sand filters complain about the fact that the filters sand gets blown into the aquarium, reducing the effectiveness of the filter. A UV sterilizer can be added to the return line of some sand filters.
Trickle filters are the best filters for the discus aquarium.
Trickle filters come with a pre-filter that first removes the sediment before the water passes over a media usually consisting of plastic balls or cubes. Large colonies of nitrifying bacteria live on this media. As long as you are pumping air into the bio ball chamber the water that passes over it will be highly oxygenated before it returns to the aquarium. A UV sterilizer can be added to the return line of the trickle filter. UV sterilizers are an excellent addition to any aquarium.