Undergravel fish tank filters have been around for a long time but these days it has been receiving a lot of bad press. While there are still some enthusiast who like the undergravel filter, a whole lot of others equate it to be a dinosaur that has no place in a modern aquarium. And who can blame them when you see the latest sponges, filter media and power filters that flood the marketplace today. But the fact is, undergravel filters are capable of doing a great filtration job “as long as they are set up properly” and that is the key phrase.
An undergravel filter consists of a raised grated platform that rests at the bottom of the aquarium. Layers of gravel is poured onto the platform, forming a porous wall between water at the top and below the platform. A tube sucks out water from beneath the platform by a pump and is poured back into the tank from the top. As the water is sucked out, water from the top is forced through the layers of gravel which filters out large debris.
There are a few factors to take note for undergravel filters to work to its maximum potential. Firstly, you need to select a platform that exactly fits the based of the aquarium. Using one that is too small will have spaces around the platform that are exposed thus not providing proper filtration.
The gravel in this type of filter is actually its filter media so it does need some attention too. It is ideal to have approximately 2 to 3 inches of gravel on top of the platform, depending on the size of the tank and the strength of the suction. It is also ideal that you have different grades of gravel, but do not choose gravel that is too tiny that it would go through the platform because it might get into the pump and ruin it. Also, make sure that the gravel is distributed evenly. Some fish love stirring up the gravel and digging holes into them, keep them even.
Do not place too many ornaments of the gravel. Remember, that’s your filter media and each ornament you place on it reduces the filtration space.
Just like any other filters, undergravel filters do need to be cleaned but for undergravel filters it is actually easier than how some people make it out to be. What you need to do is to vacuum the top of the gravel at least once a week. Since you should be doing weekly water changes, all you would need to do is run the syphon over the gravel while you are sucking out the water during the water changes and you would have killed two birds with one stone. Just make sure you don’t switch the hose around the aquarium too much so that you don’t stir up any debris.