Columnaris in discus: urgent treatment and how to tell it from fungus

In short

• Cause: Flavobacterium columnare (gram-negative) — a bacterium naturally present in aquariums.
• Lethality: the acute form kills in 24-72h — an emergency.
• Hallmark sign: fluffy white patches on the mouth and head ("cotton mouth") + lesions with red edges.
• Confusion #1: it looks like fungus (Saprolegnia) — the treatment is completely different (see below).
• Critical PARADOX: Flavobacterium multiplies faster at high temperature — do NOT raise to 32°C (90°F) as you would for Ich.
• Treatment: eSHa 2000 5 ml/50L (13 US gal) × 5 days OR Waterlife Myxazin + a stable temperature of 28-29°C (82-84°F).
• Isolation: mandatory if you have a single affected fish — extreme contagiousness.

What you'll learn from this guide

Columnaris in discus is probably the most dangerous external bacterial infection in fishkeeping — the acute form can kill an entire aquarium in 72 hours. In Symphysodon it shows as fluffy white patches on the mouth and head ("cotton mouth disease"), fins destroyed quickly and gills under attack. The biggest diagnostic problem is that it looks just like fungus (Saprolegnia) — but antifungal treatment does NOT work, and losing those 24 critical hours = mortality. This guide shows you how to clearly tell Columnaris from fungus, which antibiotics to choose (eSHa 2000, Waterlife Myxazin, Sera Baktopur Direct), why you must NOT raise the temperature (the opposite of Ich), and how to isolate affected fish correctly.

What Columnaris is — biology

Key idea: Flavobacterium lives normally in all aquariums. It becomes pathogenic when the fish is stressed (transport, acclimation) or has wounds on its body.

Triggers — what sets off Columnaris

⚠️ Most Columnaris outbreaks in discus appear 7-14 days after buying new fish — a combination of acclimation stress + new bacterial strains.

Symptoms — forms and stages

The ACUTE form (most common in discus) — EMERGENCY

Hours 0-24:

• ✅ Yellowish-white patches on the mouth and lips ("cotton mouth")
• ✅ Looks like white mold but flat and stuck on (NOT fluffy like cotton wool)
• ✅ Excess slime in the affected area
• ✅ The fish is still eating

Hours 24-48:

• ❌ The patches spread onto the head and flanks
• ❌ Bleeding around the lesion (red edges)
• ❌ The fins start to melt (associated Fin Rot)
• ❌ Rapid breathing (associated bacterial gill infections)
• ❌ Food refusal

Hours 48-72:

• ❌ Open ulcers with intense red edges
• ❌ Slime-coat loss over large areas
• ❌ The fish is lethargic, sits on the bottom
• ❌ Mortality possible

The CHRONIC form (slow progression)

• Open patches on the body that don't heal for weeks
• Progressive weight loss
• Lesions that come back after "healing"
• Slow mortality (1-2 months)

Columnaris vs fungus — THE CRITICAL DIFFERENTIATION

This is the single most important diagnosis in the guide — the treatments are completely different, and losing those 24 critical hours = mortality.

🎯 Quick test: you have a fish with a white patch on the mouth + it's at >28°C (82°F) + it was bought recently → 90% Columnaris. Start the antibiotic, don't lose 24h on an antifungal.

Treatment — step by step

Step 1 — Temperature (the critical decision)

A PARADOX vs Ich: Flavobacterium multiplies faster at high temperature.

Step 2 — Isolation (if you have 1-2 affected fish)

Columnaris is EXTREMELY contagious through water + direct contact.

1. Move the affected fish to a hospital tank (40-80L / 11-21 US gal, a sponge filter with bacteria from the main tank + 50% fresh water)
2. Treat the main tank preventively too, with a half dose of antibiotic
3. SEPARATE nets, siphon, accessories between the 2 tanks
4. Wash your hands between interventions

Step 3 — First-line antibiotic

Option A: eSHa 2000 ⭐ TOP RECOMMENDATION

Procedure:

1. Remove the activated carbon (CRITICAL)
2. Maximum aeration maintained the whole course
3. Initial dose 5 ml/50L
4. 25% change / day + proportional re-dosing (days 2-5)
5. Day 6: 50% change + new activated carbon + a vitamin supplement

Option B: Waterlife Myxazin ⭐ specific to Columnaris

• Formulated specifically for Columnaris + Fin Rot + gill infections
• Available online (EU) (approx. €19-25, Romania estimate)
• Per the manufacturer (usually 3-5 days)

Option C: Sera Baktopur Direct (severe cases)

Option D: JBL Ektol Bac Plus 250

• Per the manufacturer
• Good for mild Columnaris + associated Fin Rot
• approx. €17 / 100 ml (Romania estimate)

Option E (very severe cases): Kanamycin

• Requires a veterinary prescription
• 250-500 mg / 40 L (11 US gal)
• 5-7 days
• For cases with imminent mortality

🧮 For the exact dose on the net volume (minus substrate / decor), use the treatment calculator.

Step 4 — Salt as an adjuvant (optional)

Non-iodized salt helps with:

• Osmoregulation in a weakened fish
• Partial inhibition of Flavobacterium
• Stress reduction

Dosage for discus (sensitive):

• 1-2 g/L MAXIMUM
• 7 days maximum
• Add gradually over 2 hours (dissolved in warm water)

⚠️ Discus don't tolerate salt long-term. Use it as temporary support, not as the main treatment.

Step 5 — Recovery support (after treatment)

Recovery time:

• The patches stop spreading: 24-48h after effective treatment
• Healing of affected areas: 5-14 days
• Full recovery: 3-5 weeks
• Permanent scars possible (open spots on the body)

Common mistakes

❌ Confusing it with fungus → you treat with an antifungal for 2 days → mortality. See the differentiation table — when in doubt, treat it as a bacterium (more dangerous if you get it wrong the other way).

❌ Raising the temperature to 32°C (90°F) → you ACCELERATE Flavobacterium. Keep 28-29°C (82-84°F).

❌ Delayed treatment → the acute form kills in 24-72h. Start the antibiotic within the first 6 hours of the first suspect patch.

❌ Activated carbon during treatment → it absorbs the antibiotic, zero treatment.

❌ Large changes (>50%) in the middle of treatment → you dilute the medication.

❌ Not isolating the affected fish → the whole population exposed, extreme contagiousness.

❌ Stopping treatment "it seems better" on day 3 → the bacterium comes back aggressively in 48h.

❌ Combining eSHa 2000 + Myxazin at the same time → cumulative toxicity. Use only one.

❌ New fish added to the main tank without quarantine → Columnaris imported into your environment.

Prevention — how to avoid Columnaris

See also Simple quarantine for beginners and How to choose a healthy discus.

The Columnaris — gill infection — Fin Rot link

Flavobacterium columnare can attack 3 zones at once:

• On the skin / mouth → Columnaris (this guide)
• On the gills → bacterial gill infections
• On the fins → Fin Rot

The treatment is THE SAME (a gram-negative antibiotic + clean water + 29°C / 84°F). If you spot Columnaris on the mouth, watch the gills and fins closely — they're often affected at the same time and you'll need the complete protocol.

When to consult a specialist

• Mortality appears within <24h of the first signs
• The whole group is affected at once
• A complete treatment (5 days) doesn't work
• Recurrences after 2 apparently successful courses
• Affected fry (sensitive dosing)
• Suspected Mycobacterium (chronic weight loss + multiple lesions that don't respond)

Post on dedicated forums with photos from 3 angles (mouth, side, gills) + water parameters + the protocol you followed + a purchase history for the last 30 days — or contact breeders from the Discus.ro directory.

Final checklist — managing Columnaris

• ☐ Diagnosis confirmed (NOT fungus — brush test, yellowish color, red edges)
• ☐ Temperature checked (NOT >30°C / 86°F)
• ☐ Affected fish isolated in a hospital tank
• ☐ Main tank treated preventively with a half dose
• ☐ Activated carbon removed from both filters
• ☐ Started eSHa 2000 / Waterlife Myxazin / Sera Baktopur
• ☐ Temperature stable at 29°C (84°F)
• ☐ Maximum aeration (2 pumps)
• ☐ 25% changes / day + re-dosing
• ☐ Optional: salt 1-2 g/L in the hospital tank
• ☐ Complete treatment (5 days), NOT interrupted
• ☐ Separate nets / accessories between tanks
• ☐ Post-treatment: new carbon + vitamin supplement + a varied diet
• ☐ Monitor for 4 weeks for a relapse
• ☐ Investigated the source (new fish recently? stress?)

What to do next

📚 Continue learning:

• Saprolegnia (fungus) — a critical differentiation (white cotton wool vs yellowish patches)
• Ulcers and body wounds — lesions associated with chronic Columnaris
• Bacterial gill infections — the same bacterium on the gills
• Fin Rot in discus — a parallel manifestation
• Disinfecting the aquarium after a disease — after a severe episode

🔧 Practical resources:

• Treatment dosage calculator — eSHa 2000, Myxazin, Sera
• Visual diagnosis — at the first white patches
• Aquarium treatments — shop — eSHa, JBL, Sera, Waterlife

🐠 Final tip: Columnaris is one of the few diseases where 6 hours make the difference. If you see a white patch on a discus's mouth + the temperature was recently >30°C (86°F) + you've added new fish in the last 2 weeks → start the antibiotic NOW, don't wait for confirmation. Most losses come from 2 common errors: 1) confusing it with fungus → 24h lost on an antifungal, and 2) raising the temperature thinking it's Ich. Keep eSHa 2000 in the house at all times.