API Furan-2 is an over-the-counter aquarium antibacterial treatment containing a combination of two nitrofurans — nitrofurazone and furazolidone, often along with methylene blue in some formulations. Nitrofurans have broad-spectrum activity against many gram-positive and gram-negative bacteria and are a traditional mainstay of hobbyist fish medicine for treating fin rot, columnaris, popeye, and body ulcers. Furan-2 is an OTC aquarium product, not a prescription-grade veterinary medication. Its availability has been affected by FDA enforcement actions in some regions, so status may vary. For valuable fish or serious infections, consult an aquatic veterinarian.
Overview
Nitrofurans are reduced inside bacterial cells to reactive intermediates that damage DNA and other cellular components. This broad mechanism of action makes them effective against many bacterial pathogens, including those resistant to other antibiotics. Furan-2 is commonly used when bacterial infection is suspected but the specific pathogen is unknown, providing broad coverage.
Uses
- Bacterial fin rot
- Columnaris (cotton wool disease)
- Popeye (bacterial form)
- Body ulcers and bacterial skin infections
- Mouth fungus (often actually columnaris)
- Secondary bacterial infections following parasitic disease
- Early septicemia
Dosage
- Water dosing: 1 packet per 10 gallons of water
- Duration: One dose every 24 hours for 4 days, with a 25% water change before the final dose
- Some keepers run a longer treatment course for serious infections; follow the product label
Always follow the product label for exact dosing.
Safety Considerations
- Freshwater use — Labeled for freshwater aquariums
- Scaleless fish — Generally tolerated at standard dose but monitor closely
- Invertebrates — Not recommended for invertebrate tanks; shrimp and snails may be sensitive
- Plants — Can cause mild leaf damage in some sensitive plants; most hardy plants tolerate standard doses
- Biological filter — May affect nitrifying bacteria. Monitor ammonia and nitrite during treatment.
- Staining — Furan-2 typically tints water yellow to greenish yellow. This is normal and fades with water changes and activated carbon after treatment.
- User safety — Nitrofurans are classified as potential carcinogens. Avoid skin contact and wear gloves when dosing.
- Regulatory status — Nitrofurans are banned from use in food-producing animals in many regions. Availability as aquarium products has been affected by FDA enforcement actions.
Water Chemistry Effects
- Tints water yellow or greenish
- Minimal direct effect on pH or hardness
- Some effect on nitrifying bacteria — monitor during and after treatment
- Activated carbon removes nitrofurans — remove carbon during treatment and return afterward to clear the water tint
How to Use
- Test water and perform a water change if parameters are off
- Remove activated carbon from the filter
- Dose the correct number of packets for your tank volume
- Redose daily for 4 days, performing a 25% water change before the final dose
- Expect the water to turn yellow or greenish — this is normal
- Monitor ammonia and nitrite during treatment
- After treatment, perform a 25% water change and return activated carbon to remove residual tint
FAQs
Is Furan-2 safe for invertebrates? No, invertebrates including shrimp and snails may be sensitive. Treat in a hospital tank without invertebrates.
Why did my water turn yellow? This is normal staining from the nitrofuran compound. It will clear with water changes and activated carbon after treatment.
Can I combine it with other antibiotics? Combining antibiotics is generally not recommended without veterinary guidance.
Will it affect live plants? Most hardy plants tolerate Furan-2 at label dose, though sensitive species may show some stress.
Is Furan-2 safe for cichlids and goldfish? Yes, it is commonly used for these species at standard dose.
Do I need a prescription? Availability as an OTC aquarium product has been affected by regulatory changes. Check current status in your region.