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"King Of The Aquarium"

Discus in a 125 gallon aquarium.

By Tony Griffitts

Discus have long been know as the "King of the Aquarium." The discus is native to the Amazon and its tributaries. The discus is currently recognized as having two species and five subspecies.

  • Symphysodon discus discus - Heckel Discus
  • Symphysodon discus willischwartzi - Blue Faced Heckel Discus
  • Symphysodon aequifasciata aequifasciata - Green Discus
  • Symphysodon aequifasciata haraldi - Blue Discus
  • Symphysodon aequifasciata axelrodi - Brown Discus
Wild Discus

Above are wild Discus.  Left to right, Heckel Discus (Symphysodon discus), Green Discus (Symphysodon aequifasciata aequifasciata), Blue Discus (Symphysodon aequifasciata haraldi), and Brown Discus (Symphysodon aequifasciata axelrodi).

Although there are 5 subspecies of discus, many discus experts believe that there is only one species with many color variations.  Resent studies being done on the DNA of discus seem to support the one species theory.  Today most of the discus found in aquarium trade are domesticated, man developed color strains. It has almost become a rarity to find wild caught discus for sale.  Wild caught discus are less hardy than domestic bred discus and they often carry diseases.  Wild caught discus should only be kept by experienced discus keepers, and should be quarantined for eight weeks before you add them to your show tank.  Discus are easy to keep as long as you provide the right water conditions.  People that have problems with keeping discus are often providing the wrong water conditions, and diet. If you follow my directions  you should have no problem with keeping discus.

Man Developed Discus

Pictured above are man developed strains of Discus.  Left to right, Brilliant Turquoise Discus, Blue Diamond Discus, Pigeon Blood Discus, and Turquoise Discus.

Water Conditions

Discus come from water that is very soft, very acidic, and very warm.  To maintain discus in your home aquarium you should provide water that has a pH of 4.7 to 6.8, with a hardness of 20 to 110ppm, and a temperature of 82° to 86° F (28° to 30° ).  It is very important that you keep discus in very warm water, because they can become sick if kept at temperatures below 80° F (27° C)for an extended period of time.  Discus require frequent water changes for proper growth.  I recommend that you make 50% water changes at least once every 2 weeks for a lightly stocked aquarium, but to maximize growth at least 50% once a week or more often would be even better.  The water changes dilute the accumulation of nitrate (NO3) which is believed to be a growth inhibitor.

Selecting Your Discus

Look for discus that are full bodied and eager to eat.  Check for deformities.  The most common deformities are:

  • Short fins
  • Short gill covers
  • Misshapen eyes
  • Oval shaped
  • Short spine

Avoid discus that are brightly colored when they are smaller than 3 inches.  Healthy juvenile discus do not show strong color under 3 inches unless they are stunted or hormoned.  Healthy discus will show a color pattern at 2 inches, but the color should not be bright.  Hormoned discus should be avoided, because the procedure often causes sterility and the color will often fade within 2 months.


Discus should not be fed tubifex or black worms.  These worms carry parasites that will infest the stomach and intestines of the fish and will cause the fish to stop eating and become emaciated.  A good beef heart mixture that includes krill and vitamins are excellent food for discus.  For optimum growth, young discus should be fed 3 times a day and adults can be fed once or twice a day.  Discus can also be fed flake food, but not as a staple.

Tank Mates

Angelfish should be avoided, because they can carry internal parasites that can be passed on to discus.  When creating a discus community aquarium you should make sure that the discus are the dominant fish. No specie of fish should be added to the aquarium that can out compete discus for food.  This limits the number suitable tank mates for discus.  Here is an abbreviated list of suitable tank mates for discus:

  • Cardinal Tetra
  • Rummy-nose Tetra
  • Wild, Gold or Blue Ram
  • Black Neon Tetra
  • Apistogramma sp.
  • Rafel Catfish
  • Cory Catfish
  • Sailfin Pleco

To be safe, stick with fish that are native to the Amazon and its tributaries.


Filtration is one of the most important elements to all aquariums.  Discus prefer water that is calm, so it is important that you do not buy a filter with a high turnover rate.  For the discus aquarium, a filter with a 1 time per hour turnover rate is adequate.  For discus there are many acceptable methods of providing filtration.

Sponge Filters

Sponge filters are very common in discus hatcheries.  For the most part they are very inexpensive and provide biological and sediment filtration.  If you use a sponge filter you must clean it often with water form the aquarium. Because the sponge contains a lot of bacteria that aid in the break down of ammonia, ammonium, and nitrite it is very important that you do not clean the sponge in hot chlorinated water.  You must take care to keep the bacteria in the sponge alive.

Under Gravel Filters

Under gravel (UG) filtration has been around for many years and it is an effective biological filter as long as the gravel is spread evenly over the filter plate.  Gravel on an UG filter must be cleaned with a gravel vacuum once every two weeks to make sure that no dead spots develop and start producing hydrogen sulfide.

Power Filters

Power filters are very good at sediment filtration, but they do not provide very good biological filtration.  As long as you do not have a heavy bio-load a power filter will do the job.

Canister Filters

Canister filters are very popular mechanical filters that provide both sediment and biological filtration.  Canister filters do have some drawbacks.  Sometimes it is difficult to seal the lid on canister filters and they can leak.  If you ever have problems with getting the lid to seal you can use Vaseline on the O-ring to get a good seal.  One of the best advantages of a canister filter is that you can add an ultraviolet sterilizer (UV) to the return line.

Sand Filters

Sand filters are very effective biological filters, but they strip a lot of oxygen out of the water to convert the ammonia/ammonium and nitrite into nitrate.  The sand filter flow rate must be adjusted so that you do not blow the sand into the aquarium.  Many owners of sand filters complain about the fact that the filters sand gets blown into the aquarium, reducing the effectiveness of the filter.  A UV sterilizer can be added to the return line of some sand filters.

Trickle Filters (a.k.a. Wet Dry Filters)

Trickle filters are the best filters for the discus aquarium.  Trickle filters come with a pre-filter that first removes the sediment before the water passes over a media usually consisting of plastic balls or cubes.  Large colonies of nitrifying bacteria live on this media.  As long as you are pumping air into the bio ball chamber the water that passes over it will be highly oxygenated before it returns to the aquarium.  A UV sterilizer can be added to the return line of the trickle filter.

Ultraviolet Sterilizers (UV Sterilizers)

UV sterilizers are an excellent addition to any aquarium.  They help control parasites from spreading from fish to fish.  I highly recommend them for discus aquariums, because of the high cost of discus.  A 15 watt UV sterilizer can be bought for less than the cost of one adult discus.

How to Make Hard Alkaline Water Soft and Acidic

Hard water is usually very alkaline.  It is difficult to make hard water acidic, but it can be done with the chemicals available from many aquarium product manufacturers.  If you have a planted aquarium you will want to make sure that the product that you buy does not contain phosphate.  Phosphate promotes algae growth, therefore you should avoid it if you want to keep healthy plants.  The best way to lower the pH of your aquarium water is by using peat.  Peat can be added to canister filtration systems, on top of UG filter plates, and to the sump of a trickle filter.  Peat adds tannins to the water, turning the water a tea color.  Lowering the pH of the water is much more difficult when your water is hard. 

Use a Reverse Osmosis Filtration System (RO Unit) to make your water soft before you try to lower the pH.  An RO unit can be hooked up to your sink to provide water for your aquariums and excellent drinking water for your home. You can use large plastic trash cans with peat in nylon bags to collect the RO water, and I preheat and aerate the water before I add it to the aquariums.  There are also deionizers that can be used to soften water, but they require a lot of maintenance, and a lot more money to operate per gallon than RO units.

Published - 2000

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