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Discus look calm, but they expose every small mistake in husbandry. The good news is that most problems have clear causes and repeatable fixes. This guide shows you how to spot early warning signs, stabilize your tank, and solve the most common Discus issues before they spiral.
Introduction
Healthy Discus come from stable water, measured feeding, and low stress. When something goes wrong, symptoms often look similar. Dark color, hiding, not eating, fast breathing, and frayed fins can all point to different root causes. Start with water. Then confirm temperature, oxygen, and social stress. Only medicate when you have a likely diagnosis and a plan. This stepwise approach saves fish and money.
Core Water Parameters for Stable Discus
Temperature and Oxygen
Discus thrive at 28 to 30 C or 82 to 86 F. Warmer water holds less oxygen. Pair heat with strong surface agitation and generous filtration. A large sponge filter plus a canister or hang on back works well. In any emergency, add an airstone immediately.
pH, KH, GH, and TDS
Domestic Discus do best with a stable pH between 6.4 and 7.2. Stability matters more than chasing a target. Keep KH at a level that prevents pH swings. Aim for GH around 3 to 8 dGH and total dissolved solids around 100 to 250 ppm for most domestic strains. If your tap is very hard, blend with reverse osmosis water and remineralize to consistent targets. Avoid big pH changes during water changes.
Ammonia, Nitrite, and Nitrate
Ammonia and nitrite must stay at zero. Keep nitrate under 20 ppm, and under 10 ppm for growing juveniles. Test weekly. If numbers drift up, increase water change volume or frequency and clean detritus more thoroughly.
Filtration and the Biofilter
Cycle your filter fully before adding Discus. Seed new tanks with mature media when possible. Clean sponges and biomedia only in tank water to protect bacteria. Replace mechanical pads before they clog and reduce oxygen. Never deep clean all media at once.
Routine That Prevents Most Problems
Water Change Schedule
Juveniles need frequent large changes to grow well. Change 30 to 50 percent daily or every other day depending on feeding and stocking. Adults do well with 30 to 50 percent twice weekly. Match new water within 0.5 C or 1 F and within 0.2 pH. Always dechlorinate. Vacuum the bottom to remove waste after feedings.
Feeding Plan That Works
Use a varied diet that the fish accept readily. Good staples include quality pellets, frozen bloodworms, brine shrimp, and clean lean beef heart blends. Feed juveniles 3 to 5 small meals daily. Feed adults 1 to 2 times daily. Offer only what they eat in a few minutes and remove leftovers within 10 minutes. A weekly light feeding day can help prevent bloat. Avoid risky live feeders.
Quarantine and Biosecurity
Quarantine all new fish for 4 to 6 weeks in a separate tank. Use separate nets and buckets. Observe daily. Treat only when you see a clear problem. This one habit prevents most outbreaks in the display tank.
Stress Minimization
Keep Discus in groups of 6 or more to spread aggression. Give them space. Fifty gallons is a practical minimum for a small group. Reduce sudden noise and movement near the tank. Dim lights and provide vertical wood or plants for security. Cover side panels temporarily if fish are very skittish.
Symptom Based Troubleshooting
Dark Color, Hiding, or Clamped Fins
These signs usually mean stress. Common triggers are poor water, incorrect temperature, sudden changes, bright light, or bullying. Test water. If ammonia or nitrite is above zero, change 50 percent now and again tomorrow. Confirm temperature within the 82 to 86 F range. Lower light intensity and provide cover. Identify bullies and rearrange decor to break territories. If one fish relentlessly attacks, separate it.
Gasping at the Surface or Fast Gills
Low oxygen, heat stress, ammonia, nitrite, or gill parasites can all cause rapid breathing. Increase aeration at once. Do a large water change with matched temperature and full dechlorination. Test ammonia and nitrite. If water is perfect and breathing stays fast for more than a day, suspect gill flukes. Treat in a hospital tank with a fluke specific medication according to label and keep strong aeration during treatment.
Not Eating or Spitting Food
Rule out water quality first. Then try easier foods like frozen bloodworms to stimulate appetite. Soak dry pellets briefly to soften. Reduce stress by dimming lights and feeding when the room is quiet. If a fish refuses food for several days and passes white stringy feces or loses weight, suspect internal parasites and consider targeted treatment in quarantine. Avoid mixing multiple medications at once.
White Stringy Feces, Weight Loss, or Pinched Belly
Internal flagellates and worms are common culprits. Combine pristine water, higher oxygen, and a suitable antiparasitic plan in a hospital tank. Many keepers use metronidazole for flagellates and a dewormer such as praziquantel for tapeworms when indicated. Medicated food is often effective if the fish still eats. Follow product labels and complete the full course. Keep feeding light during treatment and maintain temperature in the mid 80s F with added aeration.
Hole In The Head and Lateral Line Erosion
Pitting around the head and along the sensory line links to chronic poor water, high nitrate, unstable minerals, and flagellates. Fix environment first. Increase water changes, keep nitrate below 10 to 20 ppm, and ensure gentle but high oxygenation. Provide a consistent mineral profile rather than ultra soft water with no buffer. Many use metronidazole in a hospital tank when flagellates are suspected. Improve diet variety and avoid long term carbon dust exposure by rinsing new carbon thoroughly or removing it during medication.
Fin Rot, Cloudy Slime Patches, or Cottony Tufts
These point to bacterial or fungal infections, often after nips or net damage. Improve water and reduce stressors. For mild cases, perfect water and time can heal fins. For progressive rot, treat in a hospital tank with an appropriate antibiotic. For cottony growths, use an antifungal. Maintain stable warm temperature and strong aeration. Remove carbon during treatment and finish the full course even if the fish looks better early.
Ich in Discus
Discus kept warm rarely get ich, but it can arrive with new fish. Raise temperature to 30 to 31 C or 86 to 88 F for a week and boost aeration. Use a proven ich medication and follow the schedule to catch new parasites as they hatch. Disinfect nets and siphons between tanks.
Flashing, Rubbing, or Excess Mucus
Flukes and other external irritants are likely when water tests fine. Start with a large water change and observe for a day. If flashing persists, use a fluke focused medication in quarantine and repeat as directed to address the life cycle. Clean the bottom well to remove eggs and debris.
Bloat, Constipation, or Dropsy
Constipation presents as swelling without pineconing and reduced feces. Offer easier foods and consider a short epsom salt bath in a hospital tank. If scales pinecone or the fish floats helplessly, this is severe organ stress. Isolate the fish, raise oxygen, and use an appropriate antibacterial plan. Outcomes are guarded. Prevention through water stability and conservative feeding is far more effective.
Stunted Growth in Juveniles
Slow growth comes from low temperature, underfeeding, crowding, and high nitrate. Keep juveniles at 84 to 86 F. Feed small meals 3 to 5 times daily. Change 30 to 50 percent of water daily or every other day. Keep nitrate under 10 ppm. Give them room and a calm environment. Consistency builds size and shape.
Peeling Slime Coat or Sudden Excess Mucus
This signals irritation from untreated tap water, temperature shock, or parasites. Confirm you dosed a conditioner that handles chlorine and chloramine. Match temperature closely during changes. Run fresh activated carbon after any suspected contaminant exposure, then remove it before medications. If mucus persists with flashing, treat for flukes in quarantine.
Setup Choices That Reduce Risk
Bare Bottom Grow Out vs Planted Display
Bare bottom tanks let you feed heavily and clean easily, perfect for juveniles. For a planted display, use moderate light, gentle flow, and hardy plants. Avoid large swings from injected CO2. Keep swimming space open. Pre filter canister inlets to stop fry or food from entering and clean pre filters weekly.
Source Water Strategy
Many domestic Discus do well in conditioned tap water if it is stable and not extreme. If your tap is very hard with high pH, consider blending with reverse osmosis and remineralizing to steady KH and GH. Avoid chasing very low pH because biofilters work poorly in extremely acidic water and pH crashes become more likely.
Temperature Strategy by Life Stage
Juveniles grow best at 84 to 86 F. Adults are comfortable at 82 to 84 F. Only raise temperature short term for specific treatments and add aeration as you heat the tank. Drop temperatures gradually when you return to normal.
Lighting and Photoperiod
Use 8 to 10 hours of gentle light. Intense light without plant cover can stress Discus and suppress feeding. Ramp lights up and down if possible. Keep the room lighting stable during feeding times.
Tank Mates
Species only tanks are easier. If you choose companions, pick calm fish that tolerate heat and avoid fin nippers. Quarantine all tank mates first. Feed Discus on their schedule and do not let faster fish outcompete them.
Maintenance Checklist
Each feeding remove leftovers. Twice a week change water and vacuum the bottom. Test ammonia, nitrite, and nitrate weekly. Clean pre filters weekly and rinse sponges in tank water. Monthly service canisters, gently swishing biomedia in old tank water. Calibrate heaters and thermometers every few months.
Medication Best Practices
Use a hospital tank. Measure actual water volume. Remove carbon and chemical resins. Add extra aeration. Dose by weight and follow the label. Treat one problem at a time. Complete the full course even if fish improve. After treatment, run carbon to clear residuals, then remove it. Log dates, doses, and observations so you can refine your approach next time.
Quick Reference Actions
If Fish Are Breathing Fast
Add an airstone, change 50 percent with matched and dechlorinated water, test ammonia and nitrite, then observe. Medicate for gill flukes only if breathing stays fast and water is perfect.
If Fish Stop Eating
Check water and temperature. Dim lights. Offer an easy food. If white stringy feces or weight loss appear, isolate and treat for internal parasites with an appropriate medication plan.
If Fins Fray or Fungus Appears
Improve water, reduce stress, and move to a hospital tank for targeted antibacterial or antifungal treatment. Keep strong aeration and finish the full course.
When to Seek Help
If multiple fish show severe symptoms, if a fish declines for 24 to 48 hours despite perfect water and oxygen, or if you cannot identify the problem, ask for help. Provide clear photos or video, full water test results, temperature, tank size, stocking, feeding schedule, and recent changes. Good data speeds up good advice.
Conclusion
Discus reward discipline. Keep temperature steady, oxygen high, water pristine, and stress low. Observe daily and act early. Solve problems in this order. Stabilize water and oxygen. Identify the most likely cause by symptom. Treat in a hospital tank with a single focused medication and complete the course. Return to a strong routine that prevents relapse. With consistency, Discus become hardy, bold, and a centerpiece you can enjoy for years.
FAQ
Q What are the ideal water parameters for Discus
A Keep temperature at 28 to 30 C or 82 to 86 F, pH stable between 6.4 and 7.2, ammonia and nitrite at zero, and nitrate under 20 ppm, ideally under 10 ppm for juveniles.
Q How often should I change water for Discus
A Change 30 to 50 percent daily or every other day for juveniles, and 30 to 50 percent twice weekly for adults, matching temperature and pH and always dechlorinating.
Q Why are my Discus dark and hiding
A Stress is likely from poor water, incorrect temperature, sudden changes, bright light, or bullying, so test water, correct temperature, reduce light, add cover, and separate any relentless bully.
Q How long should I quarantine new Discus
A Quarantine new fish for 4 to 6 weeks in a separate tank with separate equipment and observe daily, treating only when a clear problem appears.
Q What should I do if my Discus are gasping at the surface
A Increase aeration immediately, change 50 percent with matched and dechlorinated water, test ammonia and nitrite, and consider gill flukes only if breathing stays fast after water is confirmed perfect.