Fish Penicillin | Broad-Spectrum Aquarium Antibiotic | Fish Pen 500mg

Powerful Treatment for Bacterial Infections in Fish

Thomas Labs Fish Penicillin, is a broad-spectrum antibiotic formulated to combat bacterial infections in aquarium fish. This trusted fish medication is highly effective against fin rot, tail rot, and other gram-positive bacterial infections, ensuring the health and well-being of your fish in both freshwater and saltwater aquariums.

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Top Fish Penicillin Products Available

✔ Fish Pen 500mg – 30 Tablets – Ideal for treating mild bacterial infections.
✔ Fish Pen Forte 500mg – 60 Tablets – Higher dosage for moderate to severe infections.
✔ Fish Pen Forte 500mg – 100 Tablets – Bulk supply for ongoing treatment needs.

Why Choose Thomas Labs Fish Penicillin?

✔ Broad-Spectrum Antibiotic – Effective against fin rot, tail rot, and gram-positive bacterial infections.
✔ Multiple Dosage Options – Available in 30, 60, and 100 tablet packs for different treatment needs.
✔ Safe for Aquatic Use – Specially designed for freshwater and saltwater aquariums.
✔ Trusted Quality – Manufactured under strict quality standards for purity and effectiveness.

Dosage Instructions

✔ Add 1 tablet (500 mg) per 10 gallons of aquarium water.
✔ Repeat every 24 hours for 5-10 days, depending on the severity of the infection.

Usage Tips & Cautions

✔ Remove activated carbon filters during treatment for maximum effectiveness.
✔ Perform 20-25% water changes between doses to maintain water quality.
✔ Not for human use.

Related Products

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• Fish Sulfa Forte - Sulfamethoxazole 800mg, Trimethoprim 160mg (100 Tablets)
• Fish Doxycycline - 100mg (60 Capsules)

Fish Penicillin Treating Mouth Fungus Columnaris and Fin Rot

Columnaris (“Cotton mouth”) infection around a fish’s mouth: The photo shows a channel catfish with a yellowish-white bacterial growth covering its mouth – a hallmark of columnaris disease.

Despite the name “mouth fungus,” this is a bacterial infection caused by Flavobacterium columnare (formerly Flexibacter). It can also cause frayed fins and “saddleback” skin lesions. Fish Penicillin (Penicillin-G) is a classic antibiotic that some aquarists have used for columnaris and related gram-positive infections.

Penicillin works by disrupting bacterial cell wall synthesis. In cases of Flexibacter outbreaks causing fin rot or mouth lesions, penicillin can be effective in clearing the bacteria. By treating the tank with fish penicillin (in proper dosage), the cotton-like plaques on the mouth begin to clear and fins stop deteriorating, especially when combined with improved water conditions. However, penicillin has a narrower spectrum on gram-negatives, so it’s most useful when columnaris or a Streptococcus infection is confirmed.