{"product_id":"fish-pen-penicillin","title":"Fish Pen - Penicillin","description":"\u003cp\u003e\u003cmeta charset=\"utf-8\"\u003e\u003cmeta charset=\"utf-8\"\u003e\u003cem\u003eThe original broad-spectrum antibiotic — a trusted first-line treatment for gram-positive bacterial infections in freshwater ornamental fish.\u003c\/em\u003e\u003cbr\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(0, 0, 0); background-color: rgb(255, 255, 0);\"\u003eWhy choose Penicillin VK? \u003c\/span\u003e\u003c\/strong\u003e\u003cstrong\u003e\u003cspan style=\"color: rgb(0, 0, 0); background-color: rgb(255, 255, 0);\"\u003ePenicillin V Potassium (Penicillin VK) is the original and most established antibiotic class in both human and veterinary medicine. It is particularly effective against gram-positive bacteria — the organisms most commonly responsible for mouth rot, popeye, and early-stage fin rot in freshwater fish. Its long track record, predictable activity profile, and gentle impact on the aquarium ecosystem make it an ideal first-line treatment before escalating to broader or more potent antibiotics. Also known as fish pen, it remains one of the most trusted aquarium antibiotics among experienced hobbyists.\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cdiv class=\"freshwater-note\"\u003e\u003cspan style=\"color: rgb(0, 0, 0); background-color: rgb(204, 204, 204);\"\u003e\u003cstrong\u003eBest suited for freshwater tanks. Penicillin VK is most effective in freshwater aquariums. For saltwater or marine tanks, consider Minocycline or Doxycycline, which maintain stability in high-mineral and saltwater environments.\u003c\/strong\u003e\u003c\/span\u003e\u003c\/div\u003e\n\u003cdiv class=\"freshwater-note\"\u003e\n\u003cspan\u003e\u003c\/span\u003e\u003cbr\u003e\n\u003c\/div\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eAbout This Product\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003ePenicillin V Potassium (Penicillin VK) is a broad-spectrum penicillin-class antibiotic effective against a wide range of gram-positive and gram-negative bacterial microorganisms. It works by inhibiting bacterial cell wall synthesis — preventing bacteria from building the protective wall they need to survive — causing them to rupture and die. As the foundational antibiotic class, it remains one of the most effective and well-understood treatments in aquarium medicine.\u003c\/p\u003e\n\u003cp\u003eEach tablet contains USP-grade Penicillin V Potassium — available in 250mg and 500mg strengths, both in 100-tablet counts. Penicillin VK is an excellent first-line antibiotic for freshwater fish, particularly for gram-positive infections like mouth rot, popeye, and early fin rot. If treatment does not produce results within the first few days, consider stepping up to a cephalosporin (Cephalexin) or broader-spectrum antibiotic.\u003c\/p\u003e\n\u003cp\u003e\u003cem\u003eAlso commonly searched as: fish penicillin, penicillin for fish, fish pen equivalent, penicillin VK fish antibiotic, aquarium penicillin, freshwater fish antibiotic penicillin, fish pen forte equivalent.\u003c\/em\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eCommonly Treats\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eMouth rot (columnaris — early stage)\u003c\/li\u003e\n\u003cli\u003ePopeye (exophthalmia)\u003c\/li\u003e\n\u003cli\u003eFin rot \u0026amp; tail rot\u003c\/li\u003e\n\u003cli\u003eGill disease\u003c\/li\u003e\n\u003cli\u003eGram-positive bacterial infections\u003c\/li\u003e\n\u003cli\u003eBacterial hemorrhagic septicemia\u003c\/li\u003e\n\u003cli\u003eSkin infections \u0026amp; surface ulcers\u003c\/li\u003e\n\u003cli\u003eGeneral freshwater bacterial disease\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eDirections for Use\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003col\u003e\n\u003cli\u003eDetermine your dose: Use one 250mg tablet per 10 gallons of water, or one 500mg tablet per 20 gallons of water.\u003c\/li\u003e\n\u003cli\u003eDissolve the tablet in a small amount of aquarium water before adding to the tank. Stir until fully dissolved.\u003c\/li\u003e\n\u003cli\u003eAdd directly to your aquarium, pond, or hospital\/quarantine tank.\u003c\/li\u003e\n\u003cli\u003eRepeat every 24 hours for 5–10 days. Do not exceed 10 days of continuous treatment.\u003c\/li\u003e\n\u003cli\u003ePerform a 25% water change each day before re-dosing to maintain water quality and reduce antibiotic buildup.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eProduct Specifications\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003ctable class=\"specs-table\" style=\"width: 100%; height: 176.344px;\"\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eActive Ingredient\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003ePenicillin V Potassium (Penicillin VK) USP\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eAvailable Strengths\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003e250mg · 500mg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eAvailable Counts\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003e100 Tablets (both strengths)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 46.3944%;\"\u003eForm\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%;\"\u003eTablet (dissolve before use)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eAntibiotic Class\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eNatural Penicillin (Beta-lactam)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eSpectrum\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eBroad-spectrum (gram-positive emphasis, gram-negative)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eBest For\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eFreshwater ornamental fish\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003ePrescription Required\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eNo\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eGrade\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eUSP Pharmaceutical\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"height: 19.5938px;\"\u003e\n\u003ctd style=\"width: 46.3944%; height: 19.5938px;\"\u003eExpiration\u003c\/td\u003e\n\u003ctd style=\"width: 53.2446%; height: 19.5938px;\"\u003eTypically 1–3 years from manufacture date\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003cdiv class=\"warning-title\"\u003e\u003cbr\u003e\u003c\/div\u003e\n\u003cdiv class=\"warning-title\"\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eImportant Warnings \u0026amp; Cautions\u003c\/span\u003e\u003c\/strong\u003e\u003c\/div\u003e\n\u003cul class=\"warning-list\"\u003e\n\u003cli\u003eFor ornamental fish use only. Not intended for use in fish raised for human consumption.\u003c\/li\u003e\n\u003cli\u003eNot for human consumption. Do not ingest. This product is sold for aquarium fish treatment only.\u003c\/li\u003e\n\u003cli\u003eKeep out of reach of children. Store in a cool, dry place away from children and pets.\u003c\/li\u003e\n\u003cli\u003eDo not exceed 10 days of continuous treatment. Overuse may contribute to antibiotic resistance in your aquarium ecosystem.\u003c\/li\u003e\n\u003cli\u003eRemove activated carbon from your filter before treatment — carbon will absorb the medication and render treatment ineffective.\u003c\/li\u003e\n\u003cli\u003ePrimarily recommended for freshwater use. Penicillin VK can lose effectiveness in high-mineral or saltwater environments. For marine or hard water tanks, Minocycline or Doxycycline are more suitable alternatives.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cspan style=\"background-color: rgb(255, 255, 0);\"\u003e\u003cem\u003e\u003cstrong\u003e\u003cspan style=\"text-decoration: underline;\"\u003eLabel \u0026amp; Usage Disclaimer:\u003c\/span\u003e \u003c\/strong\u003ePlease read and follow all label directions before use. Product descriptions and usage instructions shown here are taken directly from the manufacturer’s product label and information provided by Montana Aquarium Supply. These statements do not represent the views or recommendations of Pittsboro Pet Supply or Pittsboro Feed. Made in the USA. Distributed by Montana Aquarium Supply – Billings, MT. \u003c\/em\u003e\u003c\/span\u003e\u003c\/p\u003e","brand":"Aquarium","offers":[{"title":"250 mg \/ 100 ct","offer_id":43092397686850,"sku":"PPS-BIN 2","price":45.28,"currency_code":"USD","in_stock":true},{"title":"500 mg \/ 100 ct","offer_id":43092397719618,"sku":"PPS-BIN 3","price":53.77,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/2680\/2846\/files\/Fish_Pen_-_Penicillin_250_mg_100_count.png?v=1773695481","url":"https:\/\/pittsboropetsupply.com\/products\/fish-pen-penicillin","provider":"Pittsboro Pet Supply","version":"1.0","type":"link"}