17.11.6. Breeding Discus

Breeding discus is a very misunderstood topic. It all has to do with what black water is. The native waters of discus are typically “black water” biotopes. Black water is water which is so low in dissolved solids that bacteria cannot grow. Bacteria need some sodium chloride and other salts in order to metabolize well and reproduce. Black water fish have special gills which can pull salts out of water with VERY low salt content. Discus are such a fish. More about this and references can be seen at this link:

17.3. Black Water Fish

There are two very pertinent videos on YouTube about breeding discus. The Jack Wattley folks swear the following is absolutely required for breeding discus:

• 35 to 80 microsiemens per centimeter conductivity (this corresponds to 23 to  54 TDS or ppm)
• pH of 5.5 to 6.5
• Ultra clean tanks vacuumed daily with 50% daily water changes
• Large wet dry filter that is very clean and obviously does little more than aerate the water

But Joey (the King of DIY on YouTube and a VERY knowledgeable hobbyist) has successfully bred discus in his “hard” tap water with the following:

• Probably roughly 150 microsiemens
• pH of 7.6
• A huge amount of mature K1 fluidized bed filtration
• Weekly 50% water changes

Huh? What gives? The answer lies in something nobody talks about – dissolved organic compounds and bacterial count in the water. Black water fish grow in water which is extremely bacteria free. So they do not have the immune systems necessary to fight off high bacterial counts in the water.

Bacteria in the water column feed on dissolved organic compounds. Bacteria attached to the surfaces of the filter media (like mature brown gunk filled K1) are in competition with the water column bacteria for those dissolved organic compounds. And a whole host of little rotifers and ciliated organisms attached to the filter media capture and eat bacteria in the water column. So there are two distinct ways to breed discus:

• Make the water so low in dissolved salts bacteria can’t multiply in the water column. Change the water very frequently. Keep the tank and the filter ultraclean with a bare bottom tank.
• Add a huge amount of filtration and prevent bacteria from living in the water column. Change the water only to maintain 80 ppm nitrate. Have a “mature” aquarium and a “mature” filter.

The interesting thing here is that there is no middle ground. 120 TDS with “good” filtration will not give optimum results.

It is a lot easier to use the “over-filtered” approach. Use very clean, over-filtered water with a pH between 7.5 and 6.0. The filter has to be mature and very good for optimum results. The breeding aquarium needs very good filtration and aeration but low water flow.  And the filter needs to be incapable of sucking in the fry. I like LARGE low flow fluidized K1 bed sumps (1x turnovers) with large 30 PPI foam prefilters over the inlets to prevent fry being sucked down to the sumps. I like the back wall of the breeding aquarium to have a good growth of algae on it.

An Unproven Hypothesis

In 2008 Crampton showed that discus in the Amazon start breeding at the beginning of the rainy season. At this time the water becomes very soft and starts to warm up. From this all the breeders have made it a “rule” that discus need very soft warm water in order to breed. This is NOT a PROVEN hypothesis. There are no experiments that have been done to confirm this to be true. And Dan Hiteshew, Joey and I have had great success not making everything warm.

Getting a Breeding pair of Discus

Getting a breeding pair of discus is not easy. One has to mix about ten discus of the same color variation in a large aquarium. Discus don’t just accept any mate like say Malawi cichlids. They are picky. When one set of discus pair up and begin mating dances they are best separated into a separate tank and kept that way for the rest of their lives. Sexing discus is NOT easy. The best way is to just let them pair off.

And, from personal experience, one has to outwit the discus to separate the paired discus. If one just tries to catch the paired discus in an aquarium with a school of discus, the pair will simply blend back into the school as soon as they see the net. One has to take an aquarium divider and ram it rapidly down between the pair and the school. Then and only then bring out the nets.

A mated pair ideally should be in a relatively small bare bottom tank. There should be a tall vertical pipe or surface, what is known as a “breeding cone”. This pipe or cone is where the discus lay their eggs. A temperature of 80⁰ and 82⁰ F. (26.6⁰ to 28⁰ C.) is optimum for breeding. It is a myth that 86⁰ F. (30⁰ C.) is needed for breeding.

The mated pair needs to be fed a high quality food with at least 50% “high quality” protein and at least 10% fat. Chopped up beef heart is the food of choice but it is very difficult to find beef heart. The salmon/spinach gel food recipe in the article below is an excellent option.

3.4. Gel Food for Aquarium Fish

Once the eggs have hatched into free swimming fry, start feeding the parents a gel food food (I like salmon and spinach) which has been blended at on high speed blend for several minutes of on and off blending. The idea is to get the particles of salmon and spinach small enough for very tiny discus fry to be able to ingest them. Note that discus are one of the few fish that “feed” their young mucous off their bodies. This unusual behavior is fascinating to watch.

4 Week Syndrome

There is a phenomenon common in discus where the discus fry all die at four weeks of age. There are all sorts of myths about it, generally having to do with flukes. They are all myths. There is no research which says flukes are the cause of the problem. No protozoans are evident on the skin or gills of dead fry, no flukes, no ich, nothing. So the next best thing is to examine what happens typically to discus fry at four weeks. Namely they are weaned off their parents mucous.

This says there is a very high probability that “4 week syndrome” is caused by suddenly weaning discus babies from their parents side feeding to “other food” whatever that might be. In the wild discus babies start picking at and eating the periphyton all around them as soon as they can swim. Yes, they eat a gel off the parents but they slowly wean off of that over the course of four weeks till at four weeks they are fully periphyton eaters.

So my breeder tanks have a mature “algae wall” in them along with two mature sponge prefilters on the sump inlets. The babies can start pecking at these as soon as they can swim. And the parents are fed a gel food that is salmon and spinach blended till it is a VERY fine consistency, quite suitable for very small mouths to eat. This gel food is fed three times a day minimum. The parents eat most of gel but the fry get a lot of it, especially as they get older.

Breeders in Asia separate the parents at three days and raise the babies on very finely blended food or daphnia. They use high volume continuous water changes instead of heavy biofiltration. It works well for them to raise decorative discus.

A good arrangement for breeding decorative discus would be the following (note there are MANY ways to do this, this is just one):

• Aquariums:
  • Two 33 gallon bare bottom aquariums set up identically. Three tanks or even more will be useful as the fry grow and the adults spawn again. Like most cichlids, once you get a breeding pair they will breed continuously for many months. After a few months the pair should be separated for four months to allow some rest. Raising kids is hard work.
  • Paint three of the walls and the floors of the aquariums with white paint.
• Filtration:
  • An air operated fluidized K1 bed 20 gallon sump under each aquarium.
  • The inflow of each of these low flow sumps is through TWO large 30 ppi sponge intake covers over TWO overflows or two drilled holes. Redundancy is important here to prevent overflows.
  • The sump pump is low flow (like 1x turnover).
• At least two air stones with at least two air pumps. Once again, redundancy is important.
• Two 25 watt heaters with an electronic controller over-ride (triple redundancy is called for here) in each sump. I take the temperature to 80 to 82 degrees F.
• An 18 watt in line UV sterilizer
• A cheap E26 bulb base 9 watt LED grow light aimed at one of the two short walls (width walls) of both aquariums. Time the light for 14 hours to 16 hours. This is to grow a wall of algae. The more algae growth the better.
• Opposite the grow light put a ceramic breeding cone.

The key to these breeding tanks is MATURITY. These tanks need to be operated as fully functioning aquarium systems for at least four months before adding any discus. After I have used my complicated (and totally unnecessary!) cycling process, I just add high protein food to these aquariums for four months with the lights on and everything running, i.e. fishless cycling with food.

This builds up all the colonies of beneficial little organisms in the fluidized bed filters. These organisms are needed for a functioning ecosystem which can deal with bacteria and things like gill fluke larvae. It also builds up a healthy wall of algae, which both the adults and the fry will browse continuously. Just be sure to change out ALL the water from both the sump and the aquarium before adding the discus.

Hobbyists think that an aquarium should be like a human’s hospital room, ultra clean and sterile. The good old “Cleanliness is next to Godliness” paradigm. Exactly the opposite is true in the “mature” aquarium. What applies in air does NOT apply in water. The idea in an aquarium is that bacteria WILL breed and multiply somewhere when you have any fish in water, it is inevitable (unless your water is VERY low in salts). The idea is to get that bacteria “eaten” in the dirty brown gunk in the filters and in the algae wall. More about this topic can be found at this link:

2.14. The “Mature” Aquarium

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Discus breeders have the same mistaken opinion that the general population does. One breeder of discus was talking about the essential use of potassium permanganate weekly in their juvenile grow out discus tanks as otherwise they get the “thirty-day” or “4 week” syndrome when all the discus fry keel over and die at thirty days of age. His discus tanks had a wet dry sump with blue plastic bioballs, neither the best filter nor the best media. The bioballs were clean as a whistle. I suspect that if this sump were a K1 fluidized bed with a lot of brown gunk in the inside of the K1, and he had algae walls in his tanks, he would not need the potassium permanganate.

The “thirty day” or “4 week” dying of fry is because the fry don’t do well when suddenly weaned to a different food. They starve for a while. While starving they are very susceptible to bacterial gill disease which can rapidly kill them. Potassium permanganate prevents the bacterial disease. But a better way is to simply insure the fry don’t have to suddenly change their diet and method of eating.

The fry do need to be able to find the parents once they hatch. This is made easier if five sides (back, two sides, bottom and top cover) of the aquarium are painted with white paint. There should be a low light on in the aquarium room during the night.

I take the adults out of the initial breeding tank and put them in the other tank at about 20 days after the fry become free-swimming, leaving the fry alone. Much longer and the fry get too irritating to the parents and can actually harm the breeding pair by biting their sides.

And one constantly hears how discus fry require live food like daphnia or brine shrimp. I’ve found that as long as one has a healthy “algae wall” the fry do just fine on salmon/spinach gel food (very well blended to reduce the particle sizes way down, see the link above) fed three times a day. Indeed it is best to feed the same gel food to the breeding adults and the fry thought the entire breeding cycle. Cichlids like discus do NOT like to have their food switched.

One must use legitimate university research on breeding discus. For instance the paper: “Effect of Water pH on the Embryonic Development of Discus, Symphysodon aequifasciatus”,  Swain et. al., 2020,

“It can be concluded that pH affects the initial eggs development and pH 6.6 can be considered best for discus egg development with minimum incubation duration and highest survival along with high hatching percentage, which can be helpful to promote successful hatchery operation.”

But one has to temper this with a close examination of the data. Here are the graphs of the data:

Both 7.36 and 6.6 pHs gave decent survival of the eggs. The difference was only about 20% (16% versus 36%). Not a huge amount. This researcher used RO water and added sodium hydroxide to raise the natural low pH of the RO water. The added sodium in the 7.36 pH water probably allowed some bacteria to breed in the water column and kill some of the eggs. This explain the difference in the 6.60 and the 7.36 pH numbers.

Joey was quite successful raising discus in his 7.6 pH tap water. But Joey had one HUGE mature fluidized K1 sump doing his filtration. One discus breeder has 8.4 pH water and does just fine. But again, the filtration amount was huge.

I am in Florida on very hard well water with a pH of 8.2. So for breeding discus I used RO water that has been re-mineralized with table salt to roughly 70 to 100 TDS. This gave me a pH that fluctuated between 6.0 and 7.0 first thing in the morning before the light got turned on. It probably isn’t necessary but that is what I did.

Note there has been a lot of research into what “triggers” spawning in discus and no research I could find has come up with anything conclusive. So just put on some Luther Vandross, dim the lights and see what happens.

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

17.11.7. Discus Aquarium Photos

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