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King Of The Aquarium

125 gallon aquarium with Discus


Published - 2000, Revised:

Discus have long been known 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).
    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.

    Although there are five subspecies of discus, many discus experts believe that there is only one species with many color variations. Recent studies on discus' DNA seem to support the one-species theory. Today most of the discus found in the 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 often carry diseases. Wild caught discus should only be kept by experienced discus keepers and should be quarantined for eight weeks before adding them to your show tank. Discus are easy to keep if you provide the right water conditions. People with problems with keeping discus often provide the wrong water conditions and diet. If you follow my directions, you should have no problem with keeping 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 110 ppm, and a temperature of 82° to 86° F (28° to 30° ). You must keep discus in very warm water because they can become sick if kept at temperatures below 80° F (27° C) for an extended period. 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), is a growth inhibitor, and has a long-term adverse effect on health.

    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 (7.5 cm). Healthy juvenile discus do not show intense 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 ensure 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 of 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 spp.
  • Cory Catfish
  • Bushy Pleco
  • To be safe, stick with fish native to the Amazon and its tributaries.


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

    Sponge Filters

    Sponge filters are widespread in discus hatcheries. Mostly they are very inexpensive and provide biological and sediment filtration. If you use a sponge filter, you must clean it often.

    Because the sponge contains a lot of bacteria that aid in the breakdown of ammonia, ammonium, and nitrite, it is essential not to sterilize it when cleaning. You must take care to keep the bacteria in the sponge alive.

    A quick cleaning in tap water will not kill the remaining bacteria on the sponge. Chlorine needs much longer contact to kill bacteria than it will receive during a quick tap water cleaning.

    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 a UG filter must be cleaned with a gravel vacuum once every two weeks to ensure no dead spots develop.

    Power Filters

    Power filters are very good at sediment filtration but only provide a little biological filtration. A power filter will work if a system does not have a heavy bio-load or has lots of surface area in the aquarium.

    Canister Filters

    Canister filters are popular mechanical filters that provide 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 getting the lid to seal, use Vaseline on the O-ring to get a good seal. One of the best advantages of a canister filter is adding 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 that the filter's sand gets blown into the aquarium, reducing the filter's effectiveness. A UV sterilizer can be added to the return line of some sand filters.

    Trickle Filters (a.k.a. Wet Dry Filters) and Sumps
    AquaMaxx AF-1 Fleece Roller
    AquaMaxx AF-1 Fleece Roller. Fleece roller mechanical filters are gaining popularity. Fleece rollers remove detritus from the system when the sensor detects the flow through the filter has been restricted. Fleece rollers remove the detritus from the system, and because of this, nitrate production will decrease. Fleece roller filters are placed inside a sump. Image from Bulk Reef Supply.

    Trickle filters are the best filters for the discus aquarium. Trickle filters come with a pre-filter that removes the sediment before the water passes over a medium, usually 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.

    Sump filtration systems are more common today (2023) without bio-media. This forces the nitrogen cycle to happen within the aquarium. Many of the sump designs use filter socks for mechanical filtration. The trend is moving to roller fleese-style systems in the sump as this type removes detritus from the system, which also slows how quickly nitrate can accumulate.

    Ultraviolet Sterilizers (UV Sterilizers)

    UV sterilizers are an excellent addition to aquariums. They are recommended for discus aquariums because of the high cost of discus. A 15-watt UV sterilizer can be bought for one adult discus. UV sterilizers help control green water algae and parasites.

    How to Make Hard Alkaline Water Soft and Acidic

    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 (DI) 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. Today, it is common to use an RO unit and then pass the water through a DI filter. These filters are called RO/DI systems.