Wet-Dry filters are a little different than the other filters on the market. The Wet dry filter is used more for biological filtration to help increase the beneficial bacteria colony in your system.
Wet/dry filters trickle water over your filter media that is suspended out of the water in the filter. The filter media is not sitting in the water. This process increases the supply of oxygen that your beneficial bacteria needs to thrive. The aquarium water then flows through another chamber or two and then returned to the aquarium through an aquarium pump and hose.
The physical make-up of a wet and dry filter varies but most are built out of acrylic and sit beneath your tank just like a sump does
on a saltwater setup. Most use some sort of continuous overflow to draw the water into the filter and an aquarium pump to return the water back into the aquarium.
Tropical Fish Tip
If you choose to use a wet dry aquarium filter on your tropical fish tank, please remember to clean your filter media often.
Clogged filter media can cause the water to overflow and drain your aquarium of its water.