Fritz Maracyn

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  • Treats bacterial infections
  • Safe for aquarium plants
  • Safe for shrimp, snails, and other invertebrates

Fritz Maracyn® is a specially compounded broad-spectrum antibiotic (erythromycin) which has been shown to be effective against a number of pathogenic bacteria associated with ornamental fish disease. It was developed for complete but gradual dissolution in water. It is primarily effective against gram-positive pathogenic organisms. Symptoms of clamped fins, swollen eyes, heavy or rapid breathing, patchy coloration, change in swimming behavior or corner-hiding can be signs of possible bacterial infection.

For the 10-count and 20-count boxes of Maracyn, the medication comes in individual packets where each packet treats 10 gallons of water. The 100-gram bulk container treats a total of 1,000 gallons of water and comes with a scoop for easy dosing. When treating with Maracyn, we recommend using an air stone in the aquarium, which may temporarily cause excessive foaming at the water surface.

Customer Reviews

Based on 532 reviews
M.V. (East Durham, NY, US)
Excellent product line

I think aquarium co-op provides an excellent online service for all my aquatic needs.

MICHAEL D. (Albuquerque, NM, US)

It does what it's supposed to do!

Sarah B. (Webster, NY, US)
Easy to use, great customer service!

I always keep Maracyn handy for suspected bacterial infections, or a real bad BG algae outbreak. Aquarium Co-Op's instructions (let sit one week) work for me 9x out of 10 if infection is caught early. Also, the only time this has wiped out my cycle was when added in combination with Paracleanse (which includes another antibiotic) AND to an immature tank. Otherwise I've never seen an issue. Love that Aquarium Co-Op has done so much testing and figured out what this can safely be combined with!

Casey (Seattle, WA, US)
Good Value

Always gotta have some on hand when you're a fishkeeper. Treats bacterial infections without hurting aquarium plants, snails, or inverts. It also doesn't color or dye the water or decorations.

Russell W. (Colorado Springs, CO, US)
Works Great

Used it in the med trio per Cory's recommendation for quarantining new fish. No problems.