Fritz Maracyn

Fritz Maracyn is a broad-spectrum erythromycin antibiotic for ornamental fish, compounded to dissolve gradually and completely in water. It targets gram-positive bacteria, the culprits behind body fungus (columnaris), bacterial gill disease, popeye, mouth fungus, open lesions, hemorrhagic septicemia, and slime disease. Packet form makes dosing simple: one packet treats 10 gallons.

Browse our full medication lineup or the rest of our Fritz range.

What It Treats

• Gram-positive bacterial infections: body fungus (columnaris), bacterial gill disease, popeye, mouth fungus, open lesions, hemorrhagic septicemia, and slime disease.
• Watch for these symptoms: clamped fins, white or fuzzy patches, cloudy eyes, frayed fins, lethargy, and fish rubbing on decor. Suspected bacterial infections should be treated promptly.
• Freshwater and saltwater: safe to use in both systems when dosed as directed.
• Pairs with Maracyn Two: if symptoms point to gram-negative bacteria, or a 5 day course brings no improvement, step up to Fritz Maracyn 2. The two can be used together for broad coverage.

Dosing

• Days 1 through 5: add the contents of one packet per 10 gallons of water every 24 hours.
• Day 6: perform a 25 percent water change.
• Repeat the 5 day course once if symptoms improved but have not fully cleared. If there is no improvement, switch to Maracyn 2.
• Remove activated carbon during treatment, keep aeration strong, and treat in a quarantine tank for best results.

Specifications

Recommended Pairings

• Cover gram-negative infections with Fritz Maracyn 2.
• Confirm water quality is not the root cause with a kit from water testing.
• Recondition after treatment with Seachem Prime.

FAQ

Maracyn or Maracyn 2, which one do I need?
Maracyn (erythromycin) targets gram-positive bacteria like columnaris and bacterial gill disease. Maracyn 2 (minocycline) targets gram-negative infections like fin rot, dropsy, and septicemia. When in doubt, bring us a photo or a water sample and we will help you narrow it down.

Do I need to remove my filter media?
Remove activated carbon only, it will strip the medication out of the water. Keep biological media running and watch ammonia, since antibiotics can knock back nitrifying bacteria.

Is it safe for plants, snails, and shrimp?
Erythromycin is generally well tolerated in planted and invert tanks when dosed correctly, but a quarantine tank is always the safer and cheaper way to medicate.

Can I use the whole 5 day course in my display tank?
You can, but a QT tank uses far less medication, protects your biofilter, and lets the sick fish recover without competition.