Internal filters sit within the tank itself and are usually attached by rubber suckers to the glass side panel but in some cases ‘hang’ on the edge of your aquarium.
Internal filters range from ‘very simple’ to complex depending upon brand and price.
Simple ‘foam’ filtration makes use of a sponge to remove particles and house beneficial bacteria, whereas the more complex filter uses a combination of a ‘sponge’ to remove ‘particles’ but also uses biological filtration with the use of ‘ceramic media’ that enhances the growth of ‘Beneficial Bacteria’. Some also come equipped with ‘Activated Carbon’ which helps keep your aquarium crystal clear. (remember to remove Carbon if you need to ‘Medicate’ your aquarium as Carbon will absorb the medication.