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Fritz | Maracyn

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Product details

Management number 235156333 Release Date 2026/07/02 List Price $6.00 Model Number 235156333
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Fritz | Maracyn

Maracyn® is a powerful antibiotic for ornamental fish, designed to combat gram-positive bacteria causing diseases like body fungus, gill disease, popeye, mouth fungus, open lesions, hemorrhagic septicemia, and slime disease. Symptoms of bacterial infections include clamped fins, swollen eyes, rapid breathing, and change in swimming behavior. If you suspect a bacterial infection, it is important to seek help from a veterinarian or fish expert and start treatment right away. The active ingredient in Maracyn® is Erythromycin.

Directions & Dosage

Add the contents of one packet per 10 gallons of water and repeat every 24 hours for 5 days. Repeat this 5 day treatment only once if needed. 

Day 1: Add the contents of one packet per 10 gallons of water.
Day 2: Add one packet per 10 gallons of water.
Day 3: Add one packet per 10 gallons of water.
Day 4: Add one packet per 10 gallons of water.
Day 5: Add one packet per 10 gallons of water.
Day 6: Repeat this five-day treatment if symptoms improve, but have not completely disappeared. If no improvement has occurred, try our Maracyn® Two and/or Maracyn® Oxy treatments.

  • For best results, use Maracyn® in a quarantine tank
  • Remove carbon during treatment, maintain adequate water flow or aeration
  • Discontinue use of skimmer during treatment if foaming is a concern
  • UV Sterilizer can be used during treatment
  • Always complete a full course of treatment, even if symptoms improve or disappear before the fifth dose
  • No contraindications: can be used with all of our other products and meds
  • Safe for use with invertebrates
  • Some more sensitive plant species may display yellowing, but this condition generally improves after the treatment; remove any plants if concerned
  • Do not perform water changes during the course of treatment. If ammonia or nitrite is a concern, detoxify during treatment with Fritz A.C.C.R. or Fritz Complete
  • Overdosed? Perform a large water change if distress is observed

Note: FOR AQUARIUM USE ONLY. Consult a veterinarian or fish expert for assistance in diagnosis of disease causing organisms and treatment options. If you are unsure of the specific infection, Maracyn® may be used concurrently with Coppersafe®, Maracyn® Two or Maracyn® Oxy.

Treating an aquarium less than 10 gallons? Check our FAQ for some quick dilution recipes or watch our instructional video below.


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