My brother's fish tank has the correct mix of fish, is clean, and is a pleasure to watch.
An aquarium is first and foremost a place where the fish will spend their entire life. Having the correct combination of species is critical to maintaining balance in a fish tank. Some fish will be more aggressive and attack smaller fish. In addition, the tank needs a well balanced mixture of bottom, middle, and top feeders to keep the tank clean of uneaten food. Aquarium expert Thomas Narten reminds us, "Not all species of fish mix well with others". My brother has a Beta that feeds on the top, tetras and lionfish to feed the middle, and catfish that live as bottom feeders. They are not aggressive and stay in their own territory. My brother has provided a well balanced environment for these fish to spend the rest of their lives in.
The fact that the fish will spend their entire lives in this tank demands that it remain clean. My brother has chosen to utilize an undergravel filter. This arrangement draws water through the gravel at the bottom of the tank and the settling debris is used to feed the plants and bottom feeders that reside there. The test of a filtering system is water clarity and in this my brother has succeeded. The water is spotless with no floating debris.