If you are looking for the best freshwater fish tank filter system, I would recommend the Eheim PRO III. It is the best fish tank filter system on the market. It has a mechanical, chemical, and biological filtration system, with three stages of filtration. This means that it uses a combination of different types of filtration to clean the water, and keeps the fish tank clean and healthy. It has five different filtration cartridges that all work together to clean the water and comes with a pump so it filters the water automatically. It is made of durable, heavy-duty components that you can count on to work for years, and it is engineered and designed to be efficient and effective. The Eheim PRO III is made to last, is built with the highest quality components, and is the best freshwater fish tank filter system on the market.