Fish Medication Guide: UK-Available Treatments and Dosing

What Is the UK Fish Medication Brands Overview?

The UK aquatics market offers several well-established medication brands that cover the full range of common fish diseases. eSHa, a Dutch brand widely available in UK aquatic shops and online, produces Exit (anti-parasite), 2000 (antibacterial and antifungal), and gdex (anti-internal parasite). These are among the most popular choices for UK fishkeepers due to their effectiveness and clear dosing instructions.

Waterlife, a British brand, offers Protozin (white spot and parasite treatment), Myxazin (antibacterial), Cuprazin (copper-based anti-parasite), and Octozin (internal parasite treatment). NT Labs provides a UK-formulated range including Anti-White Spot, Anti-Bacterial, Anti-Parasite, and Anti-Fluke. Seachem, an American brand available in UK shops, offers Paraguard, Kanaplex, and Metroplex for more targeted treatments.

Unlike in the United States, UK fishkeepers cannot purchase prescription antibiotics (such as erythromycin or kanamycin in pure form) without a veterinary prescription. However, the over-the-counter treatments available are effective for the vast majority of common diseases. If over-the-counter treatments fail, consult an aquatic veterinarian; the British Veterinary Association maintains a list of vets with fish expertise. See our equipment checklist for recommended medicine cabinet essentials.

How to Dose Fish Medication Correctly?

Accurate dosing is critical for effective treatment. Under-dosing fails to eliminate the pathogen and may promote resistance, while over-dosing can poison your fish. The first step is calculating the actual water volume of your aquarium. A tank marketed as 100 litres typically holds approximately 85-90 litres of actual water once substrate, decorations, and equipment are accounted for. Most manufacturers recommend reducing the stated tank volume by 10-15% for dosing calculations.

Before adding any medication, remove activated carbon and any chemical filtration media from your filter, as these absorb medication and reduce its effectiveness. Leave biological and mechanical filtration running to maintain water quality during treatment. Increase aeration (add an air stone or increase surface agitation) as some medications reduce dissolved oxygen levels.

Dissolve or dilute the medication in a small amount of tank water before adding it to the aquarium, and pour it near the filter outflow for even distribution. Never pour concentrated medication directly onto fish. Follow the manufacturer’s schedule precisely, including the intervals between doses, and perform water changes as specified in the instructions. Our water testing guide covers monitoring parameters during treatment.

What Are the Medication Compatibility and Mixing Risks?

As a general rule, never mix different medications simultaneously unless the manufacturer explicitly states compatibility. Combining treatments can create toxic chemical reactions, overwhelm the fish’s metabolism, and crash the biological filter. The eSHa range is a notable exception: eSHa Exit and eSHa 2000 are designed to be used together and can be dosed simultaneously for mixed infections.

If you need to switch from one medication to another (for example, if the first treatment was ineffective), perform a large water change (50-75%) and run activated carbon in the filter for 24-48 hours to remove residual medication before starting the new treatment. This clearance period prevents dangerous chemical interactions and gives the fish a recovery window.

Certain medications have specific incompatibilities. Copper-based treatments (Waterlife Cuprazin, copper medications) are toxic to all invertebrates including shrimp and snails, and should never be used in tanks containing these animals. Formaldehyde-based treatments can damage biological filtration if overdosed. Salt treatments should not be used with species sensitive to sodium (most Corydoras catfish, some tetras). Always check the specific product label for warnings. Our community fish guide identifies sensitive species.

How Should You Treat Sensitive Species and Special Cases?

Several popular aquarium fish require modified medication protocols. Scaleless fish (loaches, puffers, catfish including Corydoras) are more sensitive to chemicals because they lack the protective scale barrier that covered fish have. Most manufacturers recommend half-dosing for scaleless species. Check the specific product label, as some treatments provide explicit scaleless fish instructions.

Shrimp and snails are sensitive to many fish medications, particularly copper-based and formalin-based treatments. If your tank includes invertebrates, use only invertebrate-safe treatments or remove them to a separate container during the treatment course. eSHa 2000 and eSHa Exit are generally considered safer for tanks with invertebrates at standard doses, but always verify with the specific product label.

Fry (baby fish) and very small species are more vulnerable to medication toxicity due to their higher surface-area-to-body-mass ratio. Reduce dosing to half or one-third for fry tanks. For planted tanks, be aware that some medications (particularly copper-based treatments) can damage sensitive plant species. Remove valuable plants to a bucket of clean water during treatment if possible. Our beginner fish species guide identifies which species require special medication care.

What Is the Building a UK Fish Medicine Cabinet?

Every UK fishkeeper should maintain a basic medicine cabinet so treatment can begin immediately when disease is identified. Delays while waiting for medication delivery allow diseases to progress and become harder to treat. A well-stocked medicine cabinet includes: an anti-parasite treatment (eSHa Exit or NT Labs Anti-White Spot), an antibacterial treatment (eSHa 2000 or Waterlife Myxazin), aquarium salt (for supportive treatment and minor issues), a water conditioner (for emergency water changes), and a liquid test kit for monitoring water parameters during treatment.

Store medications in a cool, dark place and check expiry dates annually. Expired medications lose effectiveness and may produce harmful breakdown products. Replace any opened medications that are more than 12 months old, as potency degrades after opening. Keep a record of treatments administered, including dates, doses, and outcomes, which helps your aquatic vet if professional advice is needed.

Beyond medication, keep spare equipment that may be needed during emergencies: an air pump and airstone (to increase oxygenation during treatment), a small heater (for quarantine or hospital tank), and a fine-mesh net (for gently moving sick fish). Being prepared turns a potential crisis into a manageable situation. See our maintenance schedule for incorporating medicine cabinet checks into your routine.