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: The basics Stages of the nitrogen cycle Starting fishless 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. … Continue reading →