Fritz Mardel Maracyn Oxy — Oxidizing Antifungal Fish Treatment
Fritz Mardel Maracyn Oxy — Oxidizing Antifungal Fish Treatment
Mechanism: Oxidizing antifungal formula (non-antibiotic)
Maracyn Oxy acts through an oxidizing mechanism — releasing active oxygen species that disrupt fungal cell walls and kill external fungal pathogens on contact. This approach is entirely distinct from antibiotic-based Maracyn treatments: it does not contribute to antibiotic resistance and is a sound first choice when antibiotic treatment is not indicated.
What This Treats
| Pathogen / Condition | Presentation |
|---|---|
| Saprolegnia spp. | Cotton-like white or gray tufts on body, fins, or wounds — "cotton wool disease" |
| Achyla spp. | Branching fungal filaments on damaged or necrotic tissue; similar appearance to Saprolegnia |
| Fungal lesions on fish eggs | White or gray fuzzy coating spreading across spawned eggs; highly effective for egg fungus in breeding setups |
| Secondary bacterial fin rot (external) | Fin deterioration associated with fungal infection or surface tissue damage |
What Maracyn Oxy Does NOT Treat
- Internal fungal infections — this formula works on external surfaces only
- Gram-negative bacterial infections — use Fritz Maracyn 2 (minocycline) for systemic or deep gram-negative infections
- Gram-positive bacterial infections — use Fritz Maracyn (erythromycin)
- Parasites (ich, velvet, flukes, internal worms) — no antiparasitic activity
Important: Fungal Infections Are Almost Always Secondary
Saprolegnia and Achyla are opportunistic water molds — they colonize damaged, stressed, or immunocompromised tissue, not healthy intact fish. A fungal infection is a symptom, not a root cause. Identify and address the underlying issue (physical injury, fin nipping, bacterial lesion, infertile eggs) or the infection will return after treatment ends.
Treatment Protocol
- Remove activated carbon before treatment — oxidizing agents are rapidly neutralized by carbon media
- 2.5 mL per 10 US gallons (38 L), once daily for 5 consecutive days
- Perform a 25% water change before retreating if a second course is needed
- Safe for biological filtration at recommended doses
Expert guidance
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Cameron draws on 25+ years in the hobby and a marine biology background to help you choose the right fit for your system.