The purpose of your aquarium filter is to establish and maintain beneficial bacteria colonies. If you’re wondering why there needs to be bacteria in your aquarium, take a moment to learn about the nitrogen cycle:
An under-gravel filtration system is a popular choice for aquarium filtration. Here’s how they work: a plastic grid or plate sits underneath several inches of gravel. The filter draws water down through the gravel (through colonies of healthy bacteria). Lift tubes and airstones at the corners of the plate create suction and keep the water cycling.
- These filtration systems are relatively low-cost, making them a reasonable investment for new aquarium hobbyists.
- Quick and easy to set up — or quick and easy to build on your own if you like do-it-yourself projects. You don’t have to be a technical sort to set up and use an under-gravel filtration system.
- You often don’t need a lot of additional equipment for your tank if you use an under-gravel system.
However, an under-gravel filtration system is not without drawbacks.
- Under-gravel filtration limits the number of fish your aquarium can handle. Most filters can only handle one inch of fish for every five gallons of water. In a twenty gallon tank, that doesn’t translate into many fish.
- Under-gravel filtration doesn’t leave much available oxygen dissolved in the water. Oxygen is stripped out of the water by the gravel bed. Supplemental filtration may be needed to keep dissolved oxygen in the tank. Your fish may be at risk for carbon dioxide poisoning.
- Waste tends to collect in the gravel, requiring frequent cleaning. You’ll also be performing more frequent partial water changes.
- An under-gravel system can’t really be upgraded. If you decide to try more challenging (delicate) fish, you may need a whole new filtration system.
- Tanks with under-gravel filtration systems tend to have unstable pH levels. That means you’ll constantly be checking and modifying your pH levels.