They have bacteria which takes ammonia and makes it into nitrites then nitrates. This is why live plants are good for the aqaurium. The plants eat or use the nitrates. Hope I helped!
It filters the water to keep the fish disease free. Remember Finding Nemo. Get the sucker fish to clean it. You do still clean the tank once every 3 months.
filters take away big stuff like food and some fish dropings. but the filter doesnt get the stuff under the rocks. so it picks up the stuff before it hits the rocks. it also cleans the water.
