Fin Rot Treatment in Tropical Fish: UK Guide

Quick action plan

If you see ragged or frayed fins RIGHT NOW:

1. Test water (ammonia, nitrite, nitrate, pH, temperature) — fix any issues
2. 50% water change with treated tap water at correct temperature
3. Raise temperature to 26-28 °C if not already
4. Buy antibacterial medication — Esha 2000, Waterlife Myxazin, or eSHa 2000 (UK shops)
5. Dose per bottle instructions for 7-14 days
6. Daily 25% water changes during treatment (controversial but most UK keepers find it helps)
7. Remove carbon from filter during treatment

For betta-only tanks, you can add aquarium salt (1 tbsp per 20 L) alongside.

What fin rot looks like (identification)

Fin rot has clear visual signs:

Mild (early stage):

• Fin edges look slightly ragged or transparent
• Tiny white edges where tissue is dying
• Fish behaviour normal

Moderate:

• Fins visibly fraying, like they've been chewed
• Black, red, or white discoloured edges
• Fins start to shrink
• Fish slightly less active

Severe (advanced):

• Fins ragged with chunks missing
• Visible body damage where fins meet the body
• Fish very lethargic
• Loss of appetite
• Sometimes secondary infections (white spot, fungus)

Distinguishing from other problems:

• Fin nipping by other fish → clean tear, not progressive deterioration
• Fungal infection → cotton-wool tufts, not ragged edges
• Old age → very gradual fin shortening over years, no inflammation

Causes

Fin rot is opportunistic — it only attacks STRESSED fish. The trigger is almost always one of:

1. Poor water quality (60% of cases)

• Ammonia > 0.1 ppm
• Nitrite > 0.1 ppm
• Nitrate > 40 ppm
• Old water with build-up

2. Low temperature (20% of cases)

Especially with bettas. Temperature below 23 °C → immunity drops → bacteria attack fins.

3. Fin damage from tank mates (10% of cases)

• Tiger barbs, serpae tetras, some danios are notorious fin-nippers
• Damaged fin edges become infection entry points

4. Sharp decor (5% of cases)

• Fish tear fins on rough rocks, plastic plants with sharp edges
• Open wounds get infected

5. Overstocking / bullying / stress (5% of cases)

• Too many fish in too little space
• Constant chasing by aggressive tank mates

Treatment options

Option A: Antibacterial medication (recommended for community tanks)

UK products that work:

• Esha 2000 — broad spectrum, gentle, works for community tanks
• Waterlife Myxazin — established UK fin rot treatment
• eSHa 2000 (different from Esha — note spelling)
• Tetra FungiStop — for combined fin rot + fungal cases

Dose: Per bottle instructions. Typically one full dose every 24 hours for 5-7 days.

Important:

• Remove activated carbon from filter (it removes medication)
• Don't use multiple medications simultaneously
• Increase aeration during treatment
• Continue 2-3 days after symptoms vanish

Option B: Aquarium salt (for betta-only tanks)

Aquarium salt (NaCl, NOT Epsom or table salt with iodine):

• Dose: 1 tablespoon (15 g) per 20 L
• Pre-dissolve in tank water before adding
• Continue for 5-10 days
• Gradual water changes afterward to dilute over a week

Don't use salt with:

• Corydoras, kuhli loaches, scaleless fish
• Most plants (sensitive to salt)
• Shrimp and snails

Option C: Water-only treatment (mild cases)

For very early-stage fin rot (just frayed edges, no advanced damage):

1. Daily 25% water changes for 7 days
2. Raise temperature to 26-28 °C
3. Watch for improvement
4. If no improvement after 5 days, switch to medication

This works for fin rot caused purely by bad water — fix the water and the fish heals itself.

Species-specific notes

Bettas

• Most commonly affected species
• Cause is usually low temperature in unheated tanks
• Heat to 26-27 °C and add Esha 2000 + salt
• Recovery time: 4-8 weeks for full fin regrowth

Goldfish

• Often get fin rot in cold tanks (they need 18-22 °C, not tropical)
• Wrong tank temperature is often the trigger
• Salt + medication standard treatment

Plecos / Catfish

• Salt-sensitive — use medication only
• Half-dose for safety
• Often get fin rot from bullying — check for tank mate aggression

Tetras

• Half-dose medication safest
• Often the result of fin-nipping by other tetras

Discus

• Sensitive — half-dose medication
• Higher temperature (30 °C+) helps

Common mistakes

Mistake 1: Adding fin rot medication without water change first

Why it fails: The poor water that caused the fin rot is still poor. Fish remains stressed; medication treats symptom not cause.

Fix: Water change FIRST, then medication.

Mistake 2: Stopping treatment when fins look better

Why it fails: Fin rot bacteria can persist in damaged tissue. Stopping early allows regrowth of infection.

Fix: Complete the full course (7-14 days) even if fins look better at day 5.

Mistake 3: Adding salt to a tank with corydoras / loaches / shrimp

Why it fails: These species are salt-sensitive. They die before the fin rot heals.

Fix: Move sensitive species to a separate tank, OR use medication only (no salt).

Mistake 4: Using table salt instead of aquarium salt

Why it fails: Table salt has iodine and anti-caking agents, which are toxic to fish.

Fix: Aquarium salt only — buy from pet shop, sold as "aquarium salt" or "tonic salt".

Mistake 5: Treating in main tank with sensitive plants

Why it fails: Most fin rot medications kill aquatic plants and beneficial filter bacteria.

Fix: For valuable planted tanks, move affected fish to a 20 L hospital tank for treatment.

Prevention

90% of fin rot cases come from preventable issues:

1. Heater that maintains 24-26 °C (or species-appropriate temp)
2. Weekly water changes (25-30%)
3. Don't overstock (follow 60 L = max 20 small fish guideline)
4. Avoid fin-nippers (tiger barbs + flowing-finned species)
5. Smooth decor — no sharp edges
6. Quarantine new fish for 14 days
7. Don't overfeed (excess food rots → bad water)

Recovery timeline

• Days 1-3: Water change + medication, watch for behaviour improvement
• Days 5-7: Visible improvement; ragged edges stop spreading
• Day 14: Treatment complete; tissue starts regrowing
• Weeks 4-8: Full fin regrowth, often clearer/transparent at first
• Months 2-3: Colour returns to new fin tissue

Bettas with severely damaged elaborate fins may never regrow to full original size, but functional regrowth is the goal.

Summary

Fin rot is curable. Test water, fix the cause, raise temperature, add Esha 2000. Most cases resolve within 2 weeks. Prevent by maintaining clean warm water and avoiding fin-nipping tank mates.

Related guides

• Ich (White Spot) Treatment
• Why Is My Fish Swimming Sideways?
• Tropical Fish Tank Temperature
• Betta Fish Tank Mates
• Browse all freshwater fish