What is a 'wet or dry trickle filter' for an aquarium?

What is a 'wet or dry trickle filter' for an aquarium?

Marc Grover (Professional Aquarist) gives expert video advice on: Generally, how do filters work in an aquarium?; What are the best filters for a small freshwater aquarium?; What are the best filters for a large aquarium? and more...

A wet/dry filter, it's kind of as it's name implies, but it's basically a box, and part of the box, half of the box, has got a bunch of computer designed what they call "bio balls". And they are biologically designed to hold a lot of bacteria. And basically water will overflow or drain out of your tank through a tube and drop over a drip tray, which is a tray with a bunch of holes in it. And then trickle, or rain, over these bio balls. 80% of the bio balls will not be submerged at all; they'll just have this trickling effect of rain going over them. The bottom couple of inches will be submerged, of this whole box will be, especially the half with the bio balls in it, and then the water will be pumped back out either through a pump that's submerged in the other side of the filter, the open end of the box, or through an external filter that's plumbed into that open end. Wet/dry's are right now, in my opinion, the most efficient, or one of the most efficient biological filters and, again, my credo is biological filtration is at the heart of every system. And if you can have an efficient one, all the better. They are also almost maintenance free. So they work super, super well on any type of system, but they really fly and shine in a salt-water tank. I wouldn't recommend lesser filtrations for a salt-water tank, but I would recommend this filtration for a fresh-water tank. It's the king of kings; it can do all of it.