Discus Diseases

First Steps when you suspect illness or problems….

1. At the first sign of problems, the usual recommended action is to raise the temperature, gradually to 28- 30c degrees and leave their light off. If they just aren’t eating right, this is also a good first step, since the higher temp increases metabolism and can many times get them to eat again. High temperature can also help to naturally eradicate slight cases of internal parasites without requiring medication. If your fish is adult and seems to have come off his regular eating habits, don’t be too alarmed. Adult Discus sometimes may suddenly stop eating for a few days at a time. This is not extremely common, but does happen. If you suspect it’s a bacterial infection, don’t raise the temperature. (See External Parasite problems below) Be careful when adjusting temperatures, as many heaters go quickly the other way! (This will depend on your heater and size of the tank) Observe the fish for a day or so and look for further symptoms or improvement. If only one or two fish are affected in a tank of many, you may wish to move them to your hospital tank, in order to prevent possible infection of others. Medication is also more inexpensive and easier to administer in a smaller tank.

2. Try and determine what may have caused your problem…. New fish added without quarantine? ..or maybe PH Shock? PH shock is a very common problem. Even though you think you changed the water and did things right, this is a common final diagnosis for unknown stress on Discus. It’s very easy to get in a hurry and push your PH adjustment quickly with water changes, especially if you don’t use pre-treated, stored water. It may seem dumb, but it is easy to make simple mistakes like adding some chlorinated water to the tanks, too. Be careful with this, as well.

3. Old/dirty/contaminated filter elements? If you use carbon, you may have left it in too long and it suddenly released some of the contaminants it had adsorbed. Check the whole filtration system and test the water. If you see extremely high ammonia level, your carbon has probably dumped!! If you’re sure you haven’t messed up with a water change, do more water changing, paying close attention to temperature and PH.

4. Quick temperature change…. They don’t do well with fast temperature changes. Maybe you messed up with a water change and gave them colder or warmer water?? Or maybe you changed the temperature too fast with the heater. Any quick change more than a degree or two can stress them!

5. High ammonia level? Maybe your filtration system is not doing the job, or you’re feeding them too much, causing the ammonia level to rise. Have you tested the ammonia level? Perhaps too many Discus in the tank? Recommended levels are 3-4 gallons for each small one and 8-10 gallons for large ones.

6. Determine, to the best of your ability, which type of medication to try first. See the list below of diseases and recommended treatments. If you use carbon in your filtration system, remove it all. Carbon removes medications from the water! Try the medication regiment for 2-3 days. If they show no improvement, re-install your carbon (or add it) for 24 hours to remove the meds. Medications usually cannot be mixed! Do a partial water change and then try the next one you think may work (remove carbon again before use).

7. Remember, most medications deplete the available dissolved oxygen in the water, so you need to provide extra aeration while using most medications. (Add airstone(s)
Here is a list of the most common ailments and measures that can be taken to cure them…

Bacterial/External Problems

If the fish has fin rot or some type of obvious skin problem, don’t raise the temperature, but add salt at a rate of 1-2 tablespoons per 10 gallons. This can be aquarium salt, kosher salt or, as a last resort common table salt. Many external problems can be readily cured this way. Do not regularly add salt to Discus water, as is the recommendation by many for community tanks. It does, however, work well as a cure. It will dissipate with your water changes. Many medications are available for external parasite problems. Too many to list here along with the problems they cure. If your fish have extreme external problems and appear very dark, see the “Costia” section. This may be their problem.


This is a fairly common ailment with small Discus. It is an intestinal parasite, commonly brought on by even the slightest stress. If the fish look dark, have white, stringy looking white feces and are generally listless, this may be the problem. Most times they will hide in the back corner, usually facing the back of the tank. They may also have scalloped shaped portions of their fins missing. It can be fatal, but, if you have access to the medication necessary, it is most times curable. The problem is the medication can, in some cases, be hard to come buy. Unless your pet store can get it, you may need a prescription from a vet. It is a chemical used to cure worms in dogs and even humans. The human one is called Flagyl, the fish one is Metronidazole. The good part is, it’s becoming more available at pet stores. Aquatrol, Inc. markets the product as “Metrozol”. Aquatronics’ product is called “Hexamit”. Usual treatment is one capsule (250 mg) dissolved per 10 gallons of water. Do this every other day for 3 treatments. No carbon in the filters and be sure to have extra aeration in the tank, as most medications tend to lessen the oxygen in the water.

If the fish are still eating, sprinkle some of the powder on some on their food, then give it to them. Do this during the early stages of treatment, since whatever they expel can then be killed by the Metronidazole in the water so they aren’t reinfected.

Many discus keepers recommend this type of treatment as a regular routine for all new fish in their quarantine tank.

If the fish are no longer eating and you are fairly sure it’s an intestinal parasite problem, you will need to take another step with force feeding/medication. This may sound pretty weird for joe-average fishkeeper, but we disus keepers must sometimes, as you probably know by now, do some out of the ordinary things for our fish! You should only proceed with this type of treatment if you are fairly sure the fish will starve to death without doing it! It is invasive and stressful for the fish (as well as the keeper). In most cases, it works, but in some, the fish may get worse and eventually die anyway, so keep in mind it is meant only as a last effort to save the fish.

Gill Flukes…Fish may clamp one gill shut and breath heavily from the other. May also scrape themselves against tank objects in effort to dislodge the irritation. If it’s the minority of the fish in the tank, you will want to give them a “bath” in a formaldehyde type product. Put some tank water in a bucket, add a product like Kordon’s Formalin 3 (or something with formaldehyde) aerate the water in the bucket for sure, and watch them for any stress during the usually recommended 45 min. to 1 hr. treatment. Formaldehyde removes oxygen faster than most med’s, so be careful with it and remove them at any sign of stress. If you think you have an external parasite problem, this is usually a good first choice. The entire tank can be treated, if all the fish are suspect, but be aware that the water may become clouded from killing the many parasites always present! I’ve seen messages on Discus-L about good luck treating gill flukes with a product by Aquarium Products called “Life Bearer”. The package says that it will eliminate symptoms like shaking and rubbing of fish due to flukes and fish lice within 48 hrs. It is intended for use on the entire tank. Contains 0.0-dimethyl, 1-hydroxy, 2-trichloromethyl phosphonate.

When treating for flukes (in the tank) you should follow the prescribed treatment cycle, then do it again a few days or a week later, since these medications do not kill any eggs that may have been present in the tank during the first treatment. The second cycle will kill any that may have hatched after the initial treatment. If you fail to do this, your fish could become reinfected in a short time after just one treatment.

Costia… This is a secondary, or debility disease which occurs many times when your fish have suffered what may be a yet undiagnosed stress. They become dark and covered with a whitish-grey substance. They may look like their slime coat is beginning to dry up, especially along the lateral line (the line that runs laterally along the body near the top of their sides that sometimes looks like a “scratch” on their skin.) This problem is easily cured, believe it or not, with medication containing malachite green and formaldehyde. One such med available is made by Tetra and called “Contra-Spot”. I had some fish in this condition that looked so bad, I was sure they would die, but after treating, they were back to normal within 2 days!

Stomach Bloat or Constipation…Some types of foods or overeating can cause stomach bloat, but it’s not common and doesn’t last long. If the fish seems very bloated for a lengthy period, you may suspect constipation. This condition can be treated by adding Epsom salts to the water at a rate of 1 teaspoon per 5 gallons of water. If this doesn’t work, there are medications available specifically for stomach bloat conditions.

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