Internal Aquarium Filters are the easiest way to keep your fish tank clean. You just need to attached the filter to the side of your tank, fully submerged. You will clean the sponge inside each week to keep the filter clear of debris. There is a wide variety of filters on the market, but the best ones have several things in common: They can be used in fresh- and salt-water aquariums. They boast of excellent energy efficiently, are quiet while running. Check into these aquarium internal filters, and more, online.