A 20 gallon tank is a good size for the beginning hobbyist. It provides plenty of space for many different species of fish and allows the new hobbyist to create a natural-looking environment. When you set up that first 20 gallon tank, you need to make sure you use the proper filter for your needs.
A power filter is designed to hang partially inside the aquarium and partially outside. The intake tube for the filter hangs down into the water and draws that water through the filter. The water then flows up into the filter and through the cleaning cartridge, before overflowing back down into the tank in a waterfall motion. Power filters are easy to use, easy to monitor and easy to clean. All you need to do is take the cover off, lift the old filter cartridge out and replace it with a fresh one at the recommended intervals. Each filter has its own recommended replacement intervals, so read the manual and follow the recommendations.
The best thing about an in-tank filter is that it allows you to create a totally natural look in your fish tank. Some in-tank filters are designed to look like rocks, plants or pieces of wood, eliminating the need to disguise or cover up the filter. The downside of these filters is that you must unhook them and remove them from the tank to change the filter media, but this process typically only takes a few minutes.
An undergravel filter works by colonizing the friendly bacteria that consume uneaten food and fish waste. These filters can be very effective for 20 gallon aquariums and they are very easy to maintain. Performing regular water changes and vacuuming the gravel on a regular basis help the bacteria in the gravel thrive. They also provide the biological filtration needed to keep the water clean and the fish healthy. You can purchase special power heads that fit into the uptake tubes of the undergravel filter. These power heads aerate the water and make the undergravel filter more efficient.
Corner filters are designed to sit in the corner of the tank, typically at the back of the aquarium. A piece of airline tubing is attached to the corner filter; the bubbles running through it provide aeration in the water while helping the filter work more efficiently. You can use a corner filter as the only filter in a thinly-stocked 20 gallon tank or as an extra filter for an aquarium containing a large number of fish.
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