Fish Pen (Penicillin 500mg) — 60 Tablets delivers a full multi-course supply of targeted penicillin-class antibiotic treatment for ornamental and aquarium fish dealing with gram-positive bacterial infections. Each bottle contains 60 fast-dissolving tablets of 500mg Penicillin — providing enough supply for multiple complete treatment courses, making it the practical choice for fish keepers who want a reliable gram-positive bacterial antibiotic consistently on hand for ongoing ornamental fish care.
Each tablet contains 500mg of Penicillin that works by binding to penicillin-binding proteins on bacterial cell walls — blocking the final stage of bacterial cell wall synthesis and causing harmful gram-positive bacteria to rupture and die. This targeted cell wall disruption mechanism makes Fish Pen one of the most direct and proven first-line treatments when gram-positive bacterial infections are identified in freshwater or saltwater ornamental fish.
Fish Pen tablets dissolve quickly and clearly in tank water — no water discoloration — for fast and even antibiotic distribution throughout your aquarium from the very first dose. Tablets can also be crushed and mixed into fish food for medicated feeding protocols when internal bacterial delivery is preferred. Available at CalVetSupply without a vet prescription for ornamental and aquarium fish use only.
ACTIVE INGREDIENT Penicillin 500mg per tablet Tablet Count: 60 Tablets per bottle
HOW MANY TREATMENTS DOES 60 TABLETS PROVIDE?
Based on 1 tablet per 20 gallons dosing guideline. Always follow product label directions.
WHAT DOES FISH PEN TREAT?
Fish Pen (Penicillin 500mg) is effective against gram-positive bacterial conditions in ornamental freshwater and saltwater fish including:
WHY CHOOSE FISH PEN FOR GRAM-POSITIVE INFECTIONS
Fish Pen delivers focused penicillin-class treatment specifically calibrated for gram-positive bacterial pathogens — making it the most direct option when gram-positive bacteria are the confirmed cause of infection:
HOW TO USE FISH PEN
Water Treatment Method:
Medicated Feeding Method:
Important: Discontinue use and consult an aquatic veterinarian if no improvement is seen after 5 days.
WHEN TO USE FISH PEN
Fish Pen is the right choice when your ornamental fish shows:
Fish Pen targets gram-positive bacteria — for broader gram-negative coverage consider Fish Mox (Amoxicillin) or Fish Flox (Ciprofloxacin).
PRECAUTIONS & SAFETY
FAQ
Q: What is Fish Pen used for? A: Fish Pen (Penicillin 500mg) treats fin rot, mouth rot, bacterial gill disease, skin lesions, open wounds, and gram-positive bacterial infections in ornamental freshwater and saltwater aquarium fish.
Q: How many treatment courses does the 60-tablet bottle provide? A: For a 20-gallon hospital tank using 1 tablet per day the 60-tablet bottle provides up to 60 treatment days — enough for multiple complete 5–10 day treatment courses. See the treatment chart above for larger tank sizes.
Q: What is the difference between Fish Pen and Fish Mox? A: Fish Pen contains Penicillin and targets gram-positive bacteria specifically. Fish Mox contains Amoxicillin — a broader aminopenicillin that covers both gram-positive and gram-negative bacteria. Choose Fish Pen for confirmed gram-positive infections and Fish Mox when broader coverage is needed.
Q: Does Fish Pen discolor aquarium water? A: No. Fish Pen dissolves clearly and does not cause water discoloration — making it one of the cleanest fish antibiotics to use in your aquarium.
Q: Can Fish Pen be used in saltwater tanks? A: Yes. Fish Pen is effective in both freshwater and saltwater ornamental fish aquariums. Always follow label dosage directions.
Q: Is Fish Pen safe for betta fish? A: Yes. Fish Pen is safe for bettas and other small fish when dosed correctly per the label guidelines.
Q: Is Fish Pen safe for live plants? A: Yes. Fish Pen is generally safe for most live aquarium plants at recommended doses.
Q: Can Fish Pen be used with invertebrates? A: No. Penicillin may harm invertebrates such as shrimp and snails. Remove invertebrates before treatment or treat affected fish in a separate hospital tank.
Q: How long does Fish Pen treatment take? A: Treat daily for a minimum of 5 days and no longer than 10 days. Discontinue and consult an aquatic veterinarian if no improvement is seen after 5 days.
Q: Do I need a prescription to buy Fish Pen? A: No. Fish Pen is available at CalVetSupply without a vet prescription for ornamental aquarium fish use only.
