17.11.2. Filtration for Discus

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Author : David Bogert

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I found the key to decorative discus is ultra-crystal-clear water with NO bacteria counts and a HUGE amount of biofiltration. And I mean HUGE!  For decorative discus one should ideally have a sump of at least 40% of the aquarium size (a 50 gallon (189 liter) aquarium needs at least a 20 gallon (75.7 liter) sump). This sump should ideally be filled with a fluidized bed of K1 media OR layer after layer of 20 ppI Poret Foam. With decorative discus that is the ONLY filtration method I can recommend. But note many are successful with other methods. These are not “rules”.

The key for discus is to look down the length of the tank, through four or six feet of water. Are the ornaments and fish four feet away crystal clear and do they look like they are flying in air? Or is everything kind of “dull” and unclear? If it is “dull” there can be a problem. This clear water typically can only be found in over filtered aquariums whose filters have been in operation for more than four months.

The aquarium below has a slight haze to the water. Hopefully this is because the substrate was just disturbed by a water change. If that haze is “normal” these discus are probably going to have some health problems.

Discus in Less than Optimum Water
Discus in Less than Optimum Water

Bacteria free, crystal-clear water is obtained by several factors:

  • Over-filtration. Using a very good high surface area filter media in a large filter (preferably foam, K1 or pot scrubbers in a large sump, or a K1 fluidized bed sump, and definitely not a hang-on-back filter) that gives well over 100 square feet (9.29 m³) of surface area for every pound (454 gram) of fish. Note we only recommend a 2X turn-over through this sump (i.e., a 100 gallon (378.5 liter) tank with a 30 gallon (113.6 liter) sump has only a flow of 260 gallons (984.2 liter) per hour, or ([100+30 gallon] x 2) ([378.5+113.6 liter] x 2).
  • Having a filter which has been established and uncleaned for at least four months. This gets the build-up of beneficial brown gunk to the point where it can be effective.
  • Adding a UV Unit which is on 24/7 with a greater than 4 times the volume of the tank going through the sterilizer every hour. A UV unit will prevent bacteria from reproducing somewhat. But UV doesn’t remove dissolved organic compounds (DOCs) like biofiltration will. So UV should only be an adjunct to very good biofiltration.
  • Excellent aeration. Since discus like still water this can present a challenge. I do this aeration in the sump.

Obviously a program which combines any and all of these processes will give the greatest probability of success.

Symphysodon aequifasciatus Discus
Symphysodon aequifasciatus – Discus

It is important to note that 100 square feet (9.29 m³) of surface area per pound (454 gram) of fish is just one of four methods that can produce SOMEWHAT clear water.

All four methods are:

  • 100 square feet (9.29 m³) of filter media surface area per pound (454 gram) of fish
  • A polishing filter media such as Polyfil (polyester fibers), polyester mats (Pinkie Pads) or 40 ppi foam (i.e “mechanical filtration”.
  • A UV setup left on 24/7 kills the bacteria and infusoria in the water column.
  • 50% to 100% water changes every day

What is important here is the difference between “somewhat” clear and “crystal” clear. “Somewhat” clear isn’t bacteria free water. It is water where the large visible particles have been filtered out but the microscopic stuff remains. Packed polyester (Polyfil) will filter out 200 micron particles. Most infusoria will be less than 200 microns and bacteria are 2 to 8 microns in size. This “somewhat” clear water can be very unhealthy water.

Water contaminantBiofiltrationMechanical filtrationMost chemical filtrationUltraviolet
Ammonia and nitriteRemoves
Bad bacteriaRemovesRemoves
Pathogens like ichRemovesRemoves
Dissolved organicsRemoves
Feces, uneaten foodRemovesRemoves
Floating algaeRemovesRemovesRemoves
Tannic acid, dyes, smellsRemoves

Using 100 square foot (9.29 m³) of filter media surface area per pound (454 gram) of fish will produce much clearer water than the other three methods as filtration by lots of surface area and flow will eliminate something called “DOCs”, or dissolved organic compounds. Dissolved organic compounds come from food and feces and are what bacteria feed on. Polishing filter media and UV don’t eliminate DOCs so they don’t produce as clear of water. Large scale water changes only eliminate a portion of the dissolved organic compounds as feces and decaying food are producing DOCs 24/7.

Symphysodon aequifasciatus discus
Symphysodon aequifasciatus – Discus

Information on Discus

The following articles will be useful reading if you are contemplating keeping discus:

17.11. Discus

17.11.1. Discus Husbandry

17.11.2. Filtration for Discus

17.11.3. Water for Discus

17.11.4. Food for Discus

17.11.5. Discus Pheromones

17.11.6. Breeding Discus

17.11.7. Discus Aquarium Photos