Help facilitate the water flow in your fish tank with an EHEIM pump. And while you can find both internal and external versions, they both perform the same function. When comparing pumps, look for one powerful enough for your tank size, including flow rate, plumbing you plan to use, and filtration type.
Also consider whether you need a cut-off valve, which is useful on external pumps to prevent electric shock. Install an EHEIM pump and keep your fish tank algae-free.