Shop Current Fish Pen Products

The live Fish Pen & Pen Forte collection currently displays the following two tablet products:

• Fish Pen™ – Penicillin 500 mg – 30 Count;
• Fish Pen™ – Penicillin 500 mg – 60 Count.

Both current listings identify penicillin 500 mg tablets for expressly labeled ornamental and aquarium-fish applications. The principal package difference is the total tablet count.

No Fish Pen 250 mg, 100-count, capsule, powder, Aqua Pen, or separately identified original Thomas Labs product is currently displayed in this collection. Future inventory may change, so review the exact current product page before ordering.

Historical Fish Pen Penicillin 250 mg Reference

The Fish Pen name has historically been associated with penicillin 250 mg products. No 250 mg Fish Pen product is currently displayed in this collection.

Historical 250 mg references should not be used to identify or compare the currently listed 500 mg products. Before purchasing any future 250 mg listing, confirm:

• That penicillin is expressly identified as the active ingredient;
• That the listed strength is 250 mg per applicable unit;
• The number of tablets, capsules, or other units included;
• The physical product format;
• The current supplier or manufacturer;
• The intended species and application;
• The storage and handling requirements;
• The available expiration information; and
• All current warnings and purchasing restrictions.

A historical Fish Pen 250 mg product should never be confused with either of the current Fish Pen 500 mg tablet listings.

Current Fish Pen Penicillin 500 mg Tablets

The current collection is centered on penicillin 500 mg tablets in two separately identified package quantities.

Review the complete listing to confirm:

• Penicillin as the listed active ingredient;
• 500 mg per tablet;
• Either 30 tablets or 60 tablets, according to the selected product;
• Tablet format;
• The current supplier information displayed on the listing and physical package;
• The stated ornamental and aquarium-fish application;
• The current availability and checkout information; and
• All product-specific instructions, warnings, and notices.

Visit the Fish Pen & Pen Forte collection to compare the two current package sizes.

Current Package Quantities

The live collection currently displays two package options:

• 30-count bottle containing 30 penicillin 500 mg tablets;
• 60-count bottle containing 60 penicillin 500 mg tablets.

The quantity shown in the selected product title, product page, cart, checkout, order confirmation, and physical bottle determines what is included with the purchase.

Do not rely on an older product photograph, historical description, archived listing, or collection title when confirming the package count.

Alternative and Historical Penicillin Products

Aqua Pen and other penicillin-based product-family names may appear in historical references, older catalogs, or future supplier listings. No separately identified Aqua Pen product is currently displayed in this collection.

Any future alternative should be reviewed as its own product and should not automatically be considered identical to an older Fish Pen or Fish Pen Forte listing. Compare:

• The complete active ingredient;
• The listed strength per unit;
• The package count;
• The physical product format;
• The current supplier or manufacturer;
• The expressly stated ornamental-fish application;
• The official product information; and
• The storage, warning, and handling requirements.

Use only the physical labeling and current information supplied with the exact product purchased.

Thomas Labs Fish Pen Legacy

Thomas Labs was historically associated with the original Fish Pen and Fish Pen Forte product-family names. Thomas Labs is no longer operating, and original products are no longer regularly manufactured.

The current Fish Pen listings should not be represented as original Thomas Labs products unless the individual product page and physical packaging expressly identify them that way.

FishFlexFishMox continues the customer-focused Thomas Labs quality standard through clear identification of active ingredients, strengths, package quantities, formats, intended applications, and available expiration information.

Learn more on the Thomas Labs Legacy Products page.

Before ordering, verify:

• The displayed product name;
• The current manufacturer or supplier;
• The complete active ingredient;
• The listed strength;
• The package quantity;
• The physical product format;
• The current availability; and
• All current labeling and product notices.

Compare Every Product Carefully

Products within this collection may differ significantly. Before ordering, compare:

• Active ingredient: Confirm the complete penicillin ingredient identified on the product listing;
• Strength: Verify whether the product is 250 mg, 500 mg, or another expressly stated strength;
• Quantity: Confirm the number of capsules, tablets, or other units included;
• Format: The current products are tablets; verify the exact format of any future listing;
• Brand: Check the current manufacturer or supplier;
• Intended application: Confirm the species and purpose stated on the listing and label;
• Instructions: Read the directions supplied with the exact product purchased;
• Storage: Review temperature, moisture, light, and container requirements;
• Availability: Confirm that the selected product variation is currently available; and
• Restrictions: Read all applicable purchasing, shipping, and responsible-use notices.

Never select a product based only on its bottle design, capsule appearance, label color, photograph, historical name, or similarity to another listing.

Safety-Sealed Packaging

Available Fish Pen and Fish Pen Forte products may be supplied in safety-sealed bottles or other manufacturer-approved packaging.

The applicable packaging may display:

• The complete product name;
• The active ingredient;
• The listed strength;
• The package quantity;
• The intended ornamental-fish or aquarium application;
• The manufacturer or supplier;
• The expiration date;
• Storage information; and
• Important warnings or directions.

Always review the physical label and packaging supplied with the product. Do not use instructions taken from another brand, strength, package quantity, or outdated listing.

Product Availability May Change

Fish Pen and Fish Pen Forte availability may change because of:

• Manufacturer production schedules;
• Supplier inventory;
• Product discontinuations;
• Packaging or branding changes;
• Active-ingredient availability;
• Distribution and transportation conditions;
• Changes in customer demand;
• Legal or carrier restrictions; and
• Other operational considerations.

An unavailable or discontinued product may not return to stock. Any future penicillin-based alternative will be separately identified and should be reviewed according to its own current product page and physical labeling.

The addition of an alternative product does not mean that it is identical to a previously available product. Review the complete current listing before ordering.

Current Listed Expiration: 08/2027

The current Fish Pen & Pen Forte product family is listed with an expiration date of 08/2027.

Expiration dates may vary by supplier shipment, manufacturing batch, package quantity, strength, or variation. The expiration date printed on the physical product received is the final product-specific date.

The 30-count and 60-count products may come from different batches and may therefore carry different lot numbers or expiration dates.

Review the Fish Antibiotic Expiration Dates page for the current collection-level information. A specific production batch, lot number, or expiration date is not guaranteed unless expressly confirmed for the applicable order.

Product Packaging May Vary

Manufacturers and suppliers may update bottle designs, label layouts, logos, package colors, closures, safety seals, or other visual details without prior notice.

The product received may therefore look different from an older photograph while still matching the essential active ingredient, strength, quantity, format, and supplier displayed on the current product page.

Contact customer support promptly if the product received does not match the essential information shown in your order.

Inspect Products After Delivery

Before opening or using a product, inspect the shipping package, product container, label, safety seal, and contents.

Do not use the product if:

• The bottle, package, or container is broken or leaking;
• A required safety seal appears missing or compromised;
• The label is missing or unreadable;
• The product differs from the item ordered;
• The contents appear inconsistent with the listing; or
• The shipping package shows substantial damage.

Retain the product, shipping box, shipping label, and all protective packaging. Report the issue through our Contact Us page and include clear photographs.

Important Ornamental-Fish Notice

Products in this collection are intended only for ornamental fish, aquarium fish, pet fish, or another non-human application expressly identified on the applicable product page and official labeling.

Unless the official product label expressly states otherwise, products in this collection are:

• For ornamental or aquarium fish use only;
• Not intended for human use;
• Not intended for human consumption;
• Not offered as human prescription medicines;
• Not intended for food-producing fish or animals; and
• Not a substitute for professional veterinary care.

Never Use Fish Pen for Humans

Fish Pen, Fish Pen Forte, and other products offered in this collection must never be taken, administered, or used by humans.

FishFlexFishMox does not provide:

• Human medical advice;
• Human diagnoses;
• Human prescriptions;
• Human dosage recommendations;
• Pharmacy services; or
• Human treatment plans.

Anyone experiencing a human health concern should contact a licensed physician or pharmacist.

In the event of accidental exposure, ingestion, or another emergency, contact an appropriate poison-control resource or emergency service immediately.

Responsible Aquarium Care

Visible signs in aquarium fish may result from water-quality problems, temperature instability, overcrowding, environmental stress, nutritional deficiencies, parasites, injuries, or other health conditions.

The presence of visible signs does not automatically mean that a penicillin-based product is appropriate.

Before selecting any fish-care product:

• Test the aquarium water;
• Review temperature and environmental conditions;
• Observe all affected fish carefully;
• Review recent aquarium changes or additions;
• Read the complete product page and physical label;
• Confirm the stated species and application;
• Avoid combining products without appropriate professional guidance; and
• Consult a qualified veterinarian or aquatic-animal health professional when the cause is uncertain.

Consult a Qualified Professional

Professional veterinary or aquatic-animal guidance is particularly important when:

• The underlying problem cannot be identified confidently;
• Several fish are affected;
• The condition is severe, recurring, or worsening;
• The aquarium contains sensitive species;
• The fish has another known health concern;
• The animal is receiving another product;
• More than one product is being considered;
• An unexpected reaction occurs;
• The selected product has not produced the expected result; or
• The correct product or course of action is uncertain.

Our customer-support team can provide general information displayed on FishFlexFishMox.com but cannot diagnose an animal, prescribe a product, or create an individualized treatment plan.

Avoid Unapproved Product Combinations

Do not combine Fish Pen or Fish Pen Forte with other fish antibiotics, aquarium medicines, parasite-control products, supplements, or chemical treatments unless the combination is expressly supported by the applicable product instructions or directed by a qualified veterinarian.

Using several products together without appropriate guidance may:

• Increase the possibility of adverse effects;
• Affect aquarium water conditions;
• Create product interactions;
• Reduce product effectiveness;
• Affect sensitive fish or aquarium organisms; or
• Make it more difficult to identify the underlying problem.

Storage and Handling

Store each product according to the directions provided on its physical label, packaging, product page, or manufacturer documentation.

Unless different instructions are supplied, products should generally be kept:

• In their original labeled container;
• Securely closed;
• Protected from excessive heat and moisture;
• Away from direct sunlight;
• Away from children and unauthorized users;
• Separate from food and human medicines; and
• In a secure location that helps prevent accidental or unauthorized use.

Do not transfer products into unlabeled containers. Retain the original packaging for identification, instructions, expiration information, and lot details.

United States Shipping Only

FishFlexFishMox accepts and ships orders only within the United States. International shipping is not available.

Free standard U.S. shipping is available on qualifying orders over $50. Final shipping services, charges, eligibility, and delivery estimates are displayed during checkout.

Available U.S. shipping methods, costs, and estimated delivery times are displayed during checkout based on the destination, package size, product eligibility, and carrier availability.

Some products or delivery methods may not be available for every state, territory, military address, P.O. Box, or other U.S. destination.

For complete order and delivery information, review our Customer Service page.

Returns and Product Integrity

For safety and product-integrity reasons, opened, used, unsealed, altered, or partially used products are generally not eligible for return.

An eligible return must normally be:

• Unused;
• Unopened;
• In its original condition;
• In its original packaging;
• Complete with all included materials; and
• Authorized before return shipment.

Review our Return Policy before sending any product back. Unauthorized returns may be refused.

Why Choose FishFlexFishMox?

More Than 16 Years of Experience

Fish Flex Fish Mox.com has more than 16 years of experience serving aquarium keepers seeking specialized fish antibiotics and aquarium-care products.

Learn more about our store on the About Fish Flex Fish Mox.com page.

Focused Product Selection

Our catalog is centered on fish antibiotics and closely related aquarium-care products, making it easier to locate and compare relevant listings.

Clearly Identified Current Products

The current Fish Pen listings clearly identify penicillin 500 mg, tablet format, and either a 30-count or 60-count package. Review each product page and physical bottle for the final supplier, manufacturer, lot, and labeling details.

Clear Product Information

We work to present essential details such as active ingredients, strengths, package quantities, formats, suppliers, stock status, storage information, and important notices.

Careful U.S. Order Processing

Eligible in-stock orders are prepared carefully after payment authorization and any required order verification are completed.

Professional Customer Support

Our support team can assist with product availability, order status, U.S. shipping, tracking, eligible returns, and damaged-order concerns.

Explore Related Products and Collections

Compare the two current package sizes in the Fish Pen & Pen Forte collection.

Browse In-Stock Fish Antibiotics to review products currently included in that collection.

Review the Fish Antibiotic Expiration Dates page for current collection-level expiration information.

Learn about the historical product standard on the Thomas Labs Legacy Products page.

Browse the complete Fish Antibiotics collection to compare additional product families, active ingredients, strengths, formats, and package quantities.

Explore Fish Mox & Mox Forte and Fish Flex & Flex Forte for other clearly identified ornamental-fish product families.

Visit About Fish Antibiotics for educational information about product formats, selection, storage, and responsible use.

Explore the broader Medicines collection for additional available aquarium-care products.

Shop Fish Pen and Pen Forte with Confidence

Browse the Fish Pen & Pen Forte (Penicillin) collection to compare the currently displayed 500 mg tablet products in 30-count and 60-count bottles.

With more than 16 years of experience, a specialized product selection, recognized suppliers, clear information, careful U.S. order handling, and responsive customer support, FishFlexFishMox is committed to providing aquarium keepers with a dependable and professional shopping experience.