The general rule is one inch of fish per gallon of water. Gravel, rocks, plants, equipment and fish take up tank volume so the actual water volume will be less than the volume listed for the tank. Fish weight is more important than fish length. For example, the strain-on-system capacity of an eight-inch cichlid is far greater than that of eight one-inch tetras. Experienced hobbyists can safely maintain more biomass of fish in a tank than can a novice. A common exception to this rule is the Malawi (African) cichlid tank. A hobbyist can stock high numbers of these cichlids (up to one fish per gallon) in order to overcome the problems associated with territorial aggression. When this is done tanks require large filtration capacity and close attention to water quality.