This article aims to list some best practices for designing and maintaining filtration systems for freshwater aquariums.  Some or all of these may not apply to a given circumstance or size aquarium.  This article is an extension an improvement of the earlier article on Rena Filstars filters.

Redundancy

Use at least two filters that have between 75% and 100% of the required filtration capacity each.  This will provide adequate fitlration in the event of mechanical failure of one of the filters.  Also, one filter may be taken out for maintenance (cleaning, etc) without the risk of destroying the whole bio filter.

Single Purpose Filters

There are 3 primary types of filters - bio filters, mechanical filters and chemical filters.  Since each works in a very different way, and have very different maintenance requirements, separating the functions makes good sense. 

Bio filters will require nearly no maintenance, and in fact, can be harmed by it. 

Mechanical filters require frequent maintenance, as the filter media become clogged with debris.

Chemical filters have a defined useful life, which is typically short - 2 to 3 days.

Placement

The primary goal with filter placement is to ensure there are no "dead zones" where water is not moving.  Ideally, intakes and outputs will be places on opposite ends of an aquarium. to help ensure no dead spots.  Integrated filters can be placed at the sides so discharged water flows as far across the aquarium as possible.