Last Updated: June 8, 2026
TL;DR: Aquarium Melafix and Pimafix are plant-derived treatments for bacterial and fungal infections in freshwater and marine fish. Used correctly together, they cover a broad spectrum of common disease presentations with minimal impact on biological filtration.
Aquarium Melafix and Pimafix: Complete Guide to Fish Disease Treatment
Watching a healthy fish develop ragged fins, white cotton patches, or open sores is one of the more stressful moments in fish-keeping. Melafix and Pimafix — API’s most widely sold natural treatments — are frequently the first tools hobbyists reach for, and for good reason: they are effective against the most common presentations, safe for invertebrates and biological filters at labelled doses, and easy to source.
Understanding exactly what each product treats — and where they overlap — prevents the common mistake of using only one when the other is also indicated, or over-dosing in a misguided effort to accelerate recovery.
Melafix vs Pimafix: What Each Treats
Melafix (melaleuca — tea tree oil extract) targets bacterial infections. The active compounds disrupt bacterial cell membrane integrity, making it effective against gram-positive bacteria responsible for fin rot, mouth rot (columnaris in early stage), open sores, and cloudy eye with a bacterial origin.
Pimafix (pimenta racemosa — West Indian bay leaf extract) targets fungal infections. It inhibits fungal growth effectively against Saprolegnia and Achlya species — the cotton-like white or grey growths most commonly seen on wounds, eggs, and stressed fish. It also has some antibacterial activity, particularly against gram-negative organisms that Melafix covers less well.
API recommends using both products together for broad-spectrum coverage. The combination is not contraindicated — there is no documented interaction between the two extracts — and combined use reduces the risk of a mixed infection (bacterial + fungal presenting simultaneously) being only partially treated.
Top Melafix and Pimafix Products
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Dosing Guide
Both products use a 7-day treatment cycle. Dose daily for 7 days, then perform a 25% water change at the end of the cycle. If symptoms persist, repeat the cycle once.
- Melafix standard dose: 5 mL per 40 litres (10 US gallons) of aquarium water
- Pimafix standard dose: 5 mL per 40 litres (10 US gallons) of aquarium water
- Combined use: use the full dose of each independently — do not halve doses when combining
- Marine tanks: Melafix Marine (separate formulation) is available; standard Melafix is also reported effective at the same dose in reef tanks, but the marine-labelled product provides clearer usage guidance
Disease Identification and Treatment Selection Table
| Symptom | Likely Cause | Treatment | Notes |
|---|---|---|---|
| Ragged, deteriorating fins | Bacterial fin rot | Melafix | Improve water quality simultaneously |
| White/grey cotton patches on body or wounds | Fungal (Saprolegnia) | Pimafix | Often secondary to injury |
| Cottony growth on mouth | Bacterial + fungal mixed | Melafix + Pimafix | Columnaris can mimic fungal appearance |
| Cloudy eye | Bacterial infection or injury | Melafix | Check for physical damage first |
| Open sores / ulcers | Bacterial ulcer disease | Melafix + Pimafix | Serious; consider veterinary antibiotic if no improvement in 7 days |
| Fungus on eggs | Fungal (Achlya) | Pimafix (reduced dose) | Use half dose in breeding tanks |
| Ich / white spot | Parasitic (Ichthyophthirius) | Neither — use copper or formalin | Melafix/Pimafix have no anti-parasitic action |
Safety: Invertebrates, Plants, and Biological Filtration
At labelled doses, both products are generally safe for snails, shrimp, and aquatic plants. Some hobbyists report that sensitive shrimp species (Crystal Red, Caridina cantonensis varieties) show stress at full doses — consider a 50% dose reduction in shrimp-heavy setups or move shrimp to a separate vessel during treatment.
Biological filtration (nitrifying bacteria) is not significantly impacted at labelled doses. Both compounds are organic and degrade naturally; they do not accumulate in filter media in a way that disrupts the nitrogen cycle. However, remove activated carbon before and during treatment — carbon adsorbs the active compounds and renders them ineffective within hours.
For guidance on maintaining water quality during disease treatment, our aquarium water quality parameters guide covers ammonia, nitrite, and pH ranges that support recovery.
If you’re dealing with a disease outbreak in a community tank, review our quarantine tank setup guide — isolating sick fish before treatment is nearly always the better approach for protecting healthy tankmates and allowing targeted dosing.
For more serious bacterial infections that do not respond to plant-based treatments, see our overview of aquarium fish disease treatments including antibiotic options and when to involve an aquatic veterinarian.
FAQ: Aquarium Melafix and Pimafix
Can I use Melafix and Pimafix together at the same time?
Yes — API explicitly recommends combining them for broad-spectrum treatment. Add each product at its full labelled dose; they do not interact negatively and the combined antibacterial and antifungal coverage is greater than either product alone. Mix both into a cup of tank water before adding to distribute evenly.
Will Melafix or Pimafix harm my labyrinth fish (bettas, gouramis)?
There are reports, not conclusively confirmed, of Melafix causing respiratory distress in bettas and other labyrinth fish at full doses. The tea tree oil may coat the labyrinth organ’s surface and impair aerial breathing. Use a 50% dose reduction for betta-only tanks and ensure the water surface is not restricted — maximize surface area for air access during treatment.
Does Melafix treat ich (white spot disease)?
No. Melafix and Pimafix have no anti-parasitic mechanism. Ich is caused by the ciliate parasite Ichthyophthirius multifiliis and requires dedicated treatments: heat therapy, formalin, copper-based medications, or anti-parasitic medications containing malachite green. Do not delay proper ich treatment by trying plant-based remedies first.
How long do Melafix and Pimafix remain effective after opening?
The active plant extracts are stable for approximately 2 years from manufacture when stored in a cool, dark location with the cap tightly sealed. Exposure to heat above 30°C or direct sunlight accelerates oxidative degradation of the terpene compounds. Discard any product that has changed colour significantly (darkened) or developed an off-odour.
Why is my fish not improving after a full 7-day Melafix course?
Non-response after 7 days indicates either a severe bacterial infection requiring prescription antibiotics, a parasitic condition misidentified as bacterial, or ongoing poor water quality that prevents healing. Test ammonia, nitrite, nitrate, and pH before repeating treatment. If water quality is poor, a 30–50% water change with dose replenishment is more valuable than simply extending the treatment cycle.
