I recommend these internal filters because its capacity is large enough to accommodate some biological filter media that other internal filters can’t do. The flow rate and direction of the water output can be adjustable that makes this internal filter ideal for smaller tanks with small fish. If you love to use a traditional internal filter, are the best and cheapest ones to buy. They come in various sizes for aquariums up to 40 gallons.
Meet Sparky, a micro filter for fish tanks that only costs $3
In addition to removing these particles from the water column, they need to be removed from the bottom of the tank. The fins of fish often touch the bottom, and the waste particles that settle here can cause problems when the fish rubs against them. Therefore, a filter needs to draw from the tank bottom and anything it doesn't get, must be removed through siphoning. After waste has been on the tank bottom for more than a day, it has been largely broken down by the heterotrophic bacteria and turned into an unsightly, but relatively harmless mulm. At this point, it's only danger is that it will slowly increase the dissolved solids in the water, and will contribute to higher nitrates. However, it will do this whether it's on the tank bottom or sitting in a filter. Unless you clean your filter a couple time/day, it won't make much difference.
Apr 27, 2017 - Looking for a small fish tank filter
Each filter is less efficient because of some of the restrictionsplaced on filtration systems by water volume and surface area. Bothwater volume and surface area will influence the density of waste andof oxygen in the water, and this will directly impact the efficiencyof the overall. Because of the limitations on available oxygen in the water andthe rate at which waste is produced and delivered to the filter, addingmore filters will not increase the for your aquarium. This parallels the rationale behindnot using in anestablished fish tank.
Fish Tank & Aquarium Filters | PetSmart