Complete Guide to Koi Ulcer Treatment

Understanding Koi Ulcers: What Every Pond Owner Needs to Know

Koi ulcers are one of the most common and serious health issues facing pond owners. These open sores are caused by bacterial infections—primarily Aeromonas and Pseudomonas—that attack stressed or injured fish. Left untreated, ulcers can quickly become life-threatening, leading to systemic infection, organ failure, and death.

The good news? With prompt treatment and the right approach, most koi can make a full recovery. This guide will walk you through everything you need to know about identifying, treating, and preventing koi ulcers.

What Causes Koi Ulcers?

Koi ulcers don't appear out of nowhere. They're the result of a perfect storm of conditions:

Primary Causes:

• Bacterial infection - Aeromonas hydrophila and Pseudomonas fluorescens are the main culprits
• Physical injury - Scrapes from pond equipment, rocks, or aggressive fish behavior
• Parasites - Flukes, anchor worms, and lice create entry points for bacteria
• Poor water quality - High ammonia, nitrites, or pH swings weaken fish immunity
• Stress - Overcrowding, temperature fluctuations, or handling

Why Stressed Fish Are Vulnerable:

Healthy koi have a protective slime coat and robust immune system that normally keep these bacteria in check. But when fish are stressed, their defenses drop, allowing opportunistic bacteria to invade through any break in the skin.

How to Identify Koi Ulcers

Early Signs:

• Small red spots or patches on the body
• Loss of scales in specific areas
• Reddened or inflamed skin
• Clamped fins
• Lethargy or loss of appetite

Advanced Ulcers:

• Open, crater-like sores exposing muscle tissue
• White or gray edges around the wound
• Bloody or oozing lesions
• Swelling around the affected area
• Red streaking in fins or body (sign of septicemia)

Critical Warning Signs:

• Multiple ulcers spreading rapidly
• Dropsy (pinecone scales)
• Bulging eyes (exophthalmia)
• Extreme lethargy or gasping at surface

If you see critical warning signs, act immediately—these indicate systemic infection.

The Complete Koi Ulcer Treatment Protocol

Treating koi ulcers requires a multi-step approach. Here's the proven protocol used by professional koi keepers:

Step 1: Assess the Severity

Mild Ulcers (Small, superficial, fish still active):

• Can often be treated with pond-wide medication
• Fish may not need to be handled

Moderate Ulcers (Larger sores, some lethargy):

• May require isolation and direct wound treatment
• Combination of topical and systemic treatment

Severe Ulcers (Deep wounds, multiple ulcers, systemic signs):

• Requires aggressive treatment
• Isolation, direct wound care, and strong antibiotics essential

Step 2: Improve Water Quality IMMEDIATELY

Before any medication will work, you must address water quality:

1. Test your water - Check ammonia, nitrite, nitrate, pH, and KH
2. Perform a 25-30% water change - Use a quality water conditioner to remove chlorine/chloramine
3. Add beneficial bacteria - Boost your biofilter to handle waste
4. Increase aeration - More oxygen helps fish heal and supports beneficial bacteria
5. Reduce feeding - Cut back to once daily or every other day to reduce bio-load

Remember: Even the best medication won't work if water quality is poor.

Step 3: Choose Your Treatment Approach

You have several treatment options depending on severity:

For Mild to Moderate External Ulcers:

Option 1: NitroCure™ (Nitrofurazone) Bath Treatment

• Best for: First-line treatment of external ulcers, fin rot, and gill disease
• How it works: Pure nitrofurazone targets external bacterial infections
• Application methods:
  • Dip treatment (15-20 minutes) for concentrated exposure
  • Short-term bath (several hours) for moderate infections
  • Long-term bath (continuous) for ongoing treatment
• Coverage: 250g treats 66-13,000 gallons depending on method
• When to use: Start here for most new or typical external ulcers

For More Serious or Persistent External Ulcers:

Option 2: KoiCure™ (Oxolinic Acid) Immersion Treatment

• Best for: Stubborn external infections, septicemia signs, gram-negative bacteria
• How it works: Strong activity against Aeromonas and Pseudomonas
• Application: Controlled immersion or pond-wide treatment
• When to use:
  • Previous treatment didn't fully resolve the infection
  • You see red streaking in fins or body
  • Ulcers are severe, deep, or spreading
  • Signs suggest septicemia

For Severe, Resistant, or Internal Infections:

Option 3: KanaRx™ (Kanamycin Sulfate)

• Best for: Advanced cases, resistant infections, systemic involvement
• How it works: Broad-spectrum antibiotic with deep-penetrating action
• Application methods:
  • Therapeutic bath for external/systemic exposure
  • Pond immersion treatment
  • Medicated food for internal infections (critical advantage)
• When to use:
  • Fish show signs of internal infection (dropsy, swelling, bulging eyes)
  • Multiple treatments have failed
  • Infection appears resistant
  • Need to deliver antibiotic internally

Step 4: Direct Wound Care (For Moderate to Severe Ulcers)

For larger or deeper ulcers, hands-on wound treatment dramatically improves outcomes:

Supplies Needed:

• Handling net and koi sock net
• Clean koi tub with pond water
• Wound cleaning solution
• Topical antibiotic powder (optional)
• Waterproof wound sealant
• Gloves

Recommended Wound Care Products:

For professional-grade topical treatment, Aqua Meds offers:

• KoiShield
  • Powerful disinfectant and wound cleaner that prepares ulcers for treatment and prevents secondary infection

Procedure:

1. Catch and secure the fish - Use a soft koi handling net and sock net to minimize stress
2. Keep fish wet - Work quickly, keep gills submerged in oxygenated water
3. Clean the wound - Gently remove dead tissue and debris
4. Apply topical treatment - Dry antibiotic powder if recommended
5. Seal the wound - Use waterproof ointment to protect from water exposure
6. Return to isolation tank - Monitor closely for 24-48 hours

Important: Only perform direct wound care if you're comfortable handling fish. Improper handling causes more stress and can worsen the condition.

Step 5: Prevent Reinfection with Beneficial Bacteria

While treating the infection, you also need to reduce the bacterial load in your pond:

Aqua Medzyme™ (Dry or Liquid)

• How it works: Competitive exclusion—beneficial bacteria starve out Aeromonas and Pseudomonas
• Benefits:
  • Reduces pathogenic bacteria to harmless levels
  • Prevents new infections
  • Supports healing
  • Enhances biofilter performance
• When to use: Start during treatment and continue for prevention
• Temperature range: Works down to 40°F

This creates a healthier pond environment that prevents future outbreaks.

Step 6: Monitor and Adjust

Daily Monitoring:

• Check ulcer appearance - Is it healing or spreading?
• Observe fish behavior - Appetite, activity level, breathing
• Test water parameters - Maintain stable, optimal conditions
• Watch for new ulcers on other fish

Signs of Improvement (within 3-5 days):

• Ulcer edges begin to heal inward
• Redness decreases
• Fish becomes more active
• Appetite returns

Signs Treatment Isn't Working:

• Ulcer continues to spread
• New ulcers appear
• Fish becomes more lethargic
• Red streaking appears (septicemia)

If treatment isn't working: Step up to a stronger antibiotic or consult a koi health professional.

Treatment Decision Tree

New, Small, External Ulcers:
→ Start with NitroCure™ bath treatment + water quality improvement

Stubborn or Spreading External Ulcers:
→ Move to KoiCure™ immersion treatment

Severe, Deep, or Internal Infections:
→ Use KanaRx™ (bath + medicated food if fish is eating)

Prevention & Long-Term Health:
→ Add Aqua Medzyme™ to reduce pathogenic bacteria

Can You Use Multiple Antibiotics Together?

No. Do not use NitroCure, KoiCure, and KanaRx at full strength simultaneously. This can:

• Stress the fish
• Damage your biofilter
• Make it impossible to know what's working

However, you CAN use them sequentially:

1. Start with NitroCure for external infections
2. If response is incomplete, move to KoiCure
3. Reserve KanaRx for severe or resistant cases

You can also combine antibiotics with beneficial bacteria (Aqua Medzyme) and wound care products.

How Long Does Treatment Take?

Mild ulcers: 5-7 days with visible improvement in 3 days

Moderate ulcers: 7-14 days, may require multiple treatment rounds

Severe ulcers: 2-4 weeks, often requires combination therapy

Important: Complete the full treatment course even if the ulcer looks better. Stopping too early allows bacteria to return.

Preventing Future Ulcer Outbreaks

Once you've treated the current outbreak, focus on prevention:

1. Maintain Excellent Water Quality

• Test weekly (ammonia, nitrite, nitrate, pH, KH)
• Perform regular water changes (10-20% weekly)
• Keep filters clean and well-maintained
• Ensure adequate aeration

2. Reduce Stress

• Avoid overcrowding (follow stocking guidelines)
• Minimize handling
• Provide shade and hiding spots
• Maintain stable water temperature
• Quarantine new fish for 3-4 weeks

3. Control Parasites

• Monitor for flukes, anchor worms, and lice
• Treat parasite outbreaks promptly
• Parasites create entry points for bacteria

4. Use Beneficial Bacteria Regularly

• Add Aqua Medzyme or similar products bi-weekly
• Reduces pathogenic bacteria populations
• Supports biofilter health
• Especially important in spring and fall

5. Feed Quality Food

• High-quality pellets with immune-boosting ingredients
• Don't overfeed (uneaten food degrades water quality)
• Reduce feeding in cold weather

6. Seasonal Preparation

• Spring: Start beneficial bacteria early, watch for spring ulcer syndrome
• Summer: Monitor oxygen levels, increase aeration in heat
• Fall: Boost beneficial bacteria as temperatures drop
• Winter: Use cold-water bacteria (Arctic Blend or Dual Blend)

When to Call a Professional

Seek expert help if:

• Multiple fish are affected
• Ulcers are spreading rapidly despite treatment
• Fish show signs of systemic infection (dropsy, bulging eyes)
• You're unsure about diagnosis
• Treatment isn't working after 7 days
• You're uncomfortable handling fish for wound care

Common Mistakes to Avoid

❌ Treating without fixing water quality - Medication won't work in poor water

❌ Using expired or low-quality medications - Use pharmaceutical-grade products

❌ Stopping treatment too early - Complete the full course

❌ Mixing multiple antibiotics at once - Use sequentially, not simultaneously

❌ Ignoring other fish - Monitor the entire pond for signs of infection

❌ Forgetting about parasites - Check for and treat parasites first

❌ Over-handling sick fish - Minimize stress during treatment

Final Thoughts

Koi ulcers are serious, but they're treatable. The key is acting quickly, choosing the right treatment for the severity, and addressing the root cause—whether that's water quality, parasites, or stress.

Remember:

1. Fix water quality first
2. Start with appropriate antibiotic for severity
3. Monitor daily and adjust as needed
4. Prevent future outbreaks with good husbandry

With the right approach, your koi can make a full recovery and thrive for years to come.

Need help choosing the right treatment? Contact us or consult our medication comparison guide for detailed guidance.