Identify, treat, and prevent common discus fish diseases. Clear symptoms, proven cures, dosing tips, and prevention routines to keep your discus thriving.

Diseases of Discus Fish and Their Cures: The Complete, Practical Guide

Discus fish (Symphysodon spp.) are breathtaking, intelligent, and social—often called the “kings of the aquarium.” But their beauty comes with exacting requirements. Native to slow, warm, soft Amazon waters, discus thrive only when water quality is pristine, stress is low, and nutrition is consistent. Even small lapses can open the door to parasites, bacterial bloom, or “mystery” syndromes that spread quickly through a group.

This guide gives you a practical, field-tested roadmap: how to recognize symptoms early, match them to the likely cause, apply evidence-based treatments (with dosing notes and timelines), and build a prevention routine that keeps disease out of your system. Use it as your go-to reference whenever a fish acts “off.”

Quick Match: Symptom → Likely Cause

• • White, stringy feces; not eating; holes on head: Hexamita / HITH
  • Gasping, rapid gill movement, scraping: Gill flukes
  • Salt-grain dots on skin/fins, flashing: Ich
  • Fine golden “dust,” clamped fins, light sensitivity: Velvet
  • Sudden gray patches on skin, heavy slime coat: Costia/Chilodonella
  • Frayed/necrotic fins: Fin rot (bacterial)
  • White cottony growth on wounds: Saprolegnia (fungus)
  • Mouth fuzz/“saddleback” lesion: Columnaris (bacterial)
  • Red streaks, ulcers, pop-eye: Septicemia (bacterial)
  • Sunken belly or wasting despite eating: Internal worms
  • Turned very dark, heavy mucus, stops eating: “Discus plague”-like syndrome
  • Bloating, trouble staying upright: Swim bladder/constipation

Top Discus Diseases and Practical Cures

Important: Always medicate in a separate hospital tank when possible, with strong aeration and no carbon/UV. Follow product labels for your exact concentration and fish load.

1.   Hole-in-the-Head / Hexamitiasis (HITH)

Cause: Protozoa (often Hexamita/Spironucleus), compounded by stress/poor diet.

Core signs: Tiny pits around the head/lateral line, white stringy feces, weight loss, appetite crash.

Treatment plan

• • Metronidazole bath (common dose ~250–400 mg per 10 gal / ~25–40 mg/L) every 24–48h for 5–7 days after a 25–50% water change each time.
  • Food-soak metronidazole for targeted gut action (if fish are still eating).
  • Nutritional rehab: High-quality protein, vitamin-rich foods (spirulina, beef-heart blends), B-complex + vitamin C, and garlic as an appetite trigger.
  • Sanitation: Siphon waste daily; hold stable temp on the warm end (84–86°F).

Prevention: Avoid chronic nitrate creep, keep diet varied, quarantine all new fish.

2.   Gill & Skin Flukes (Dactylogyrus, Gyrodactylus)

Signs: Heavy breathing, one gill closed, gill flaring, flashing, clamped fins; sometimes clear excess mucus.

Treatment plan

• • Praziquantel (commonly 2 mg/L as a prolonged bath; many use PraziPro). Repeat in 5–7 days to hit hatch-outs.
  • Salt dips (short, controlled) can reduce parasite load between main treatments.
  • Aeration: High! Parasites and meds both stress respiration.

Prevention: Quarantine with a prophylactic deworming protocol; keep stocking density modest.

3.   Ich (White Spot Disease)

Signs: Sugar-grain white cysts on skin/fins/gills; scratching; appetite loss.

Treatment plan

• • Raise temp gradually to ~86°F to accelerate the free-swimming stage (the only stage meds hit).
  • Ich meds (malachite green, formalin/malachite blends, or copper). Discus tolerate copper carefully—monitor and never mix with inverts.
  • Daily partial changes and gravel-vac during outbreak.

Prevention: Avoid sudden cold drafts/water changes; quarantine all new stock.

4.   Velvet (Oodinium)

Signs: Fine golden/bronze dust under light, rapid gilling, clamped fins, photosensitivity.

Treatment plan

• Copper-based treatment per label; closely monitor.
• Darken tank (parasite is photosynthetic).
• Raise temp moderately; boost aeration.

Prevention: Quarantine plants/fish; avoid light shock.

5.   Costia / Ichthyobodo & 6) Chilodonella (External Protozoa)

Signs: Sudden grayish film, heavy slime coat, lethargy, edge fraying on fins, huddling near filter output.

Treatment plan

• Formalin or formalin/malachite green per label, or salt (measured, short dips) as supportive.
• Maintain excellent oxygenation—these parasites hammer the gills.
• Repeat doses to cover life cycles; vacuum detritus to limit reinfection.

Prevention: Keep organic load low, especially in warm water.

6.   Columnaris (Flavobacterium) a.k.a. “Mouth Fungus” (but bacterial)

Signs: White fuzzy growth on mouth/edges (“cotton”), “saddleback” lesion across the dorsal area, frayed fins, rapid decline in warm water.

Treatment plan

• Antibiotics with gram-negative coverage (check local availability: kanamycin, nitrofurazone, or combination kits labeled for Columnaris).
• Keep cool end of discus range (82–84°F) during treatment; very high heat can accelerate Columnaris.
• Aggressive sanitation and oxygen.

Prevention: Minimize net/handling injuries; don’t allow detritus buildup.

7.   Fin Rot (Bacterial Complex)

Signs: Fin edges whiten then fragment; rays become ragged; secondary fungus may appear.

Treatment plan

• Water quality reset: 40–50% change daily for several days.
• Broad-spectrum antibacterials (per label).
• Add catappa leaves or humic substances to support mucous and recovery.

Prevention: Clean, stable water; reduce fin-nipping tankmates.

8.   Saprolegnia (True Fungus)

Signs: Cotton-like tufts on wounds or eggs; follows injury/stress.

Treatment plan

• Antifungal baths (malachite green blends, salt dips).
• Debride (gently) if directed by a vet; keep fish isolated and stress-free.
• Fix root cause (abrasive decor, bullying, ammonia burn).

9.   Bacterial Septicemia (Aeromonas, Pseudomonas, etc.)

Signs: Red streaks in fins, ulcers, hemorrhaging, pop-eye; fish isolates and stops eating.

Treatment plan

• Targeted antibiotics (as permitted locally; kanamycin, oxytetracycline, or dedicated gram-negative mixes).
• Epsom salt in a hospital tank (low dose) can help with osmoregulation in pop-eye cases.
• Frequent water changes; strict hygiene.

Prevention: Avoid spikes (ammonia/nitrite), keep nets/equipment disinfected between tanks.

10.   Internal Worms (Camallanus, Capillaria, Tapeworms)

Signs: White stringy feces, wasting/sunken belly (Capillaria) or bloat (tapeworm), reduced growth.

Treatment plan

• Levamisole HCl (common hobby bath dose ≈2 mg/L) or praziquantel for cestodes; repeat per life cycle (7–14 days).
• Food-based dewormers, if fish are still feeding, follow the label strictly.
• Thorough substrate vacuum to remove eggs.

Prevention: Quarantine; avoid unvetted live foods.

11.   “Discus Plague”-Like Syndrome (Mixed Etiology)

Signs: Very dark coloration, clamped fins, heavy mucus, faeces stop, rapid group spread.

Treatment plan

• Supportive care: pristine water, heat on the warmer side (84–86°F), very high aeration.
• Broad-spectrum antibacterials for secondary infections.
• UV sterilizer (post-crisis) can help limit pathogen load.
• Keep lights low; reduce handling.

Prevention: Biosecurity—never mix groups from unknown sources without a full quarantine.

12.   Cloudy Eye / Pop-Eye (Exophthalmia)

Signs: Hazy cornea or bulging eye(s); often secondary to trauma/water issues.

Treatment plan

• Water quality correction first.
• Epsom salt (magnesium sulfate) is used in a hospital tank at a modest dose to reduce fluid pressure.
• Antibiotics if bacterial involvement is suspected.

Prevention: Gentle netting, obstacle-free scape, stable parameters.

13.   Swim Bladder Trouble & Constipation

Signs: Fish tilts, struggles to maintain position; often linked to overeating dry foods or gut inflammation.

Treatment plan

• Fasting 24–48h, then feed deshelled pea or high-fiber frozen foods.
• Epsom salt (low dose) to ease constipation.
• Review diet variety and feeding frequency.

Prevention: Soak dry pellets, rotate diets, and avoid binge feedings.

Hospital Tank: 10-Step Treatment Protocol

1. 1. Set up a bare hospital tank (sponge filter, heater, lid, air stone).
   2. Match the temperature/pH to the display tank; avoid additional stress.
   3. Move only the sick fish (or entire group if pathogen spreads readily).
   4. Remove carbon/zeolite/UV (they strip meds).
   5. Dose per label; more is not better.
   6. Super-aerate—most meds lower dissolved oxygen.
   7. Daily partial water changes before each redose cycle.
   8. Observe appetite, respiration, stool, and coloration—log changes.
   9. Redose appropriately to catch life cycles (flukes, protozoa, worms).
   10. Rest & rebuild: after cure, run carbon for 24–48h, add vitamins/probiotics, then return fish once vigorous.

Medication & Support Cheat-Sheet (for quick reference)

• • Metronidazole (HITH/Hexamita): Bath + food-soak; multiple days with pre-change.
  • Praziquantel (flukes/tapeworms): Prolonged bath; repeat in 5–7 days.
  • Copper (velvet/ich): Precisely dosed; test frequently; no inverts.
  • Formalin/Malachite Green (ich/costia/chilodonella): Use with robust aeration.
  • Nitrofurazone / Kanamycin / Erythromycin (bacterial): Choose based on signs; observe label interactions.
  • Salt: Short dips for external parasites; not a constant in soft-water species.
  • Epsom Salt: Gut motility/edema support in hospital only.
  • Catappa/Blackwater: Mild antibacterial support, stress reduction.
  • Tip: Always verify compatibility when combining meds, and adjust for total water volume (substrate, decor, and equipment displace water).

Prevention: Your Weekly & Monthly Routine

Daily (2–3 minutes):

• Observe each fish: breathing, fins, stool, appetite, and social behavior.
• Remove uneaten food within 5–10 minutes.

Weekly:

• 25–50% water change (breeding/grow-out can be more frequent).
• Gravel-vac to remove organics; wipe biofilm from glass.
• Test ammonia, nitrite, nitrate, and pH.
• Rinse sponge filters in tank water (never tap).

Every New Addition (Non-Negotiable):

• Quarantine 4–6 weeks in a separate system.
• Prophylactic fluke/worm treatment if your source is mixed.
• Never share nets/siphons between the QT and the display.

Nutrition & Immunity:

• Rotate high-quality pellets, frozen mysis/brine, beef-heart blends, blackworm (vetted source).
• Add vitamins 2–3× weekly; garlic to trigger appetite during recovery.
• Don’t overfeed—small, frequent meals are safer than big dumps.

Final Word

Most discus losses aren’t “mystery deaths”—they’re the endpoint of stress + instability + delayed treatment. Flip that script: stabilize water, observe daily, act early with a hospital tank, and support recovery with nutrition and oxygen. Do that consistently and you’ll keep your kings healthy, colorful, and confident long-term.

FAQs

Why do my discus keep getting sick even with water changes?

Large, infrequent changes help, but instability between changes (temperature swings, pH drift, overfeeding) still stresses fish. Aim for smaller, steadier changes and keep bio-load modest. Test weekly; don’t let nitrate creep above 20 ppm.

Can I treat discus in my planted display tank?

You can, but it’s risky. Copper and some dyes harm plants/inverts and disrupt bio-filters. A hospital tank preserves your aquascape and lets you dose precisely without collateral damage.

My fish has white poop—is it worms or Hexamita?

White, stringy stool + head pits → Hexamita is likely. White stool + sunken belly or wasting → internal worms likely. In practice, many hobbyists tackle Hexamita first, then deworm if signs persist.

How hot should I go for parasite treatment?

Most parasite protocols run best at 84–86°F. Raise temperature slowly (1°F per 6–12h) and boost aeration. Don’t spike heat with antibiotics for Columnaris; it can worsen outcomes.

Are salt baths safe for discus?

Short, measured salt dips are useful for external parasites, but discus are soft-water fish—avoid long-term salinity in the main tank.

What is “discus plague,” and can I cure it?

It’s a catch-all name for a highly contagious syndrome (often mixed infections plus stress). There’s no single “silver bullet.” Success depends on biosecurity, supportive care, and treating secondary bacteria while holding perfect water and oxygen.

How long should I keep the new discus in quarantine?

4–6 weeks. Observe eating, feces, breathing, and color daily. Many keep a prophylactic fluke/worm schedule in QT before any display-tank contact.

Can diet really prevent disease?

Absolutely. A varied, vitamin-rich diet (plus lean protein and roughage) strengthens the mucous barrier and immune function, making infections less likely to take hold or recur.

When should I call a vet?

If you see rapid systemic decline, massive ulcers, or unresponsive outbreaks after correct dosing, a fish-health professional can culture and prescribe targeted antibiotics legally and safely.