The rule that we go by for a standard home aquarium is one Discus fish or angelfish per 8 gallons of water. This number can vary quite a bit depending on the filtration used on the discus/angelfish tank and the size of the discus/angelfish in the tank. In most of our 55 gallon grow out tanks in our hatchery, we keep up to 24, 3-4 inch discus fish or angelfish in each tank!. . that is one per two gallons.. This may seem extreme, but there is a continual flow of water in and out of the discus tanks at a rate of five gallons a minute. This water is filter by 8 foot fluidized bed sand filters along with a wet dry biological bed.
Along with this we do water changes of 30% every other day to keep up with the huge bio load. Keep in mind that Discus fish are great jumpers so make sure to keep there tanks well covered… The Discus fish are all fed 4-5 times a day making sure that they all get a full bellies worth at each meal. We feed the younger discus fish a diet of HBH discus pellet food, frozen bloodworms, chiclid delight, several different types of HBH flake food, enriched frozen brineshrimp, mysis shrimp, live blackworms and frozen daphnia.
The reasons for these high stocking densities is that it cuts the Discus fishes territorial fighting behavior down to nothing. Discus kept in numbers lower than one per eight gallons can be prone to this territorial bickering, making them spend more time defending there territories than putting energy into growth. Once we begin to pair our discus or angelfish off we will cut there tank numbers down to one per 10 gallons… Once they have paired off we remove them to one pair per 29 gallon aquarium.