Kordon Methylene Blue is a trusted, broad-spectrum aquarium treatment that has been protecting fish from fungus, parasites, and respiratory distress for over 60 years. Available in a 4 fl oz (118 mL) hobbyist bottle or a 1 Gallon (3.8 L) shop-and-breeder size, it is safe for both freshwater and saltwater aquariums and is a staple of any hobbyist’s quarantine and disease-prevention kit.
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Why Hobbyists Trust Methylene Blue
- Anti-fungal & disease prevention— controls fungus on fish and prevents fungal growth on freshly-laid fish eggs.
- Treats nitrite & cyanide poisoning— restores oxygen-carrying capacity of blood when fish suffer from “brown blood” disease.
- Mild parasite support— helps with external protozoan parasites including ich (white spot) and velvet when used as a dip or bath.
- Freshwater & saltwater safe— formulated to work in both systems, ideal for quarantine tubs.
- Two sizes— 4 fl oz treats up to 360 gallons; the 1 Gallon size is sized for breeders, shops, and large quarantine systems.
Dosing & Usage
Standard tank dose:1 teaspoon (5 mL) per 10 gallons of aquarium water. Repeat every 3 days with a partial water change in between if needed.
Fish bath / dip:1 teaspoon (5 mL) per 5 gallons in a separate container; bathe fish for up to 10 seconds to several minutes depending on tolerance.
Egg fungus prevention:Add to a hatching tank at the standard dose to prevent fungus on developing eggs.
Important:Methylene Blue will stain silicone, decorations, and clothing blue. Use in a quarantine or hospital tank when possible.Do notuse in a display tank with biological filtration — it can harm beneficial nitrifying bacteria. Not safe for live plants or invertebrates.
Specifications
| Brand | Kordon |
| Product | Methylene Blue — General Disease Prevention |
| Sizes | 4 fl oz (118 mL) and 1 Gallon (3.8 L) |
| Coverage (4 oz) | Treats up to 360 gallons |
| Active Ingredient | Methylene Blue (USP) |
| Water Type | Freshwater & Saltwater |
| Use For | Fungus, ich, velvet, nitrite poisoning, egg protection |
| Reef / Plant Safe | No — quarantine tank only |
Recommended Pairings
- Safety Stop Rapid Fish Quarantine Bath — pair with Methylene Blue for thorough new-fish quarantine.
- Polyp Lab Medic — reef-safe ich & velvet treatment for display saltwater tanks.
- Hikari PraziPro — pairs well for flukes and internal parasites in quarantine.
- Seachem Prime 250 mL — water conditioner for setting up your QT system.
- Water testing kits — monitor your QT parameters during treatment.
Frequently Asked Questions
Is methylene blue safe for plants and invertebrates?
No. Methylene Blue can damage live plants, snails, shrimp, and other invertebrates. It will also disrupt biological filtration. Always dose in a separate quarantine or hospital tank.
Will it stain my silicone or decorations?
Yes — methylene blue is a strong dye and can permanently tint silicone seals, plastics, and porous decor. Use a dedicated QT setup with bare-bottom or expendable hardware whenever possible.
How often can I redose?
Standard practice is to redose every 3 days alongside a 25% water change. Continue treatment for 5–7 days or until symptoms resolve.
Can I use it in a saltwater reef display?
No. Methylene Blue is not reef-safe. For display reefs, use a reef-safe option like Polyp Lab Medic instead.
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