Koi Medication & Treatments

Everything you need to keep your koi healthy, in one place. Whether you're fighting a parasite outbreak, healing an ulcer, or simply building a pond first-aid kit, our koi medications cover the conditions hobbyists actually face, from ich, flukes and anchor worm to bacterial ulcers, fin rot and fungus.

New to koi health? Start with the symptom finder below. Match what you can see on your fish to the right treatment. And remember the golden rule: test your water before you medicate. Most "sick" koi are really stressed by their water, and the fix is often a water change, not a bottle.

Shop by condition

Know what you're treating? Jump straight to the right shelf.

🐛Parasites & IchWhite spots, flashing & velvetShop these 🪱Flukes & WormsGill/skin flukes & tapewormsShop these ⚓Lice & Anchor WormVisible crawling parasitesShop these 🦠Bacterial & UlcersSores, fin & mouth rotShop these 🍄FungusCotton-like growth on skin or finsShop these 🩹Wound CareHealing, slime coat & antisepticsShop these 💤AnestheticSafe sedation for handlingShop these 💧Water QualityAmmonia, chlorine & preventionShop these

What's your koi doing? Find the right treatment.

New to koi health? Start with what you can see. Match the symptom to a card, then pick the treatment that fits.

Before you medicate: test your water first.

The great majority of "sick koi" are really stressed by their water, not by a bug. Ammonia, nitrite, low oxygen and pH swings cause flashing, clamped fins, gasping and even ulcers. A test kit is the cheapest, most useful thing a new hobbyist can own. Fix the water, and often the fish recovers on its own. If readings are clean and symptoms persist, work down the cards below.

Parasites · protozoa
Flashing, rubbing & white spots

You see: koi darting and scratching against rocks, clamped fins, excess slime, or grains of "salt" (white spots) on the skin and fins.

Likely cause: external protozoan parasites such as ich (white spot), costia, trichodina, chilodonella or velvet.

Reach for ProForm-C KoiRx Terminate Nox-Ich
Parasites · flukes & worms
Flicking with nothing to see & laboured gills

You see: flashing and clamped fins but no white spots, fast or heavy gill movement, koi hanging listlessly, sometimes thin despite eating.

Likely cause: gill & skin flukes (microscopic) or internal tapeworms.

Reach for FlukeGuard Aqua-Prazi Praziquantel
Bacterial infection
Ulcers, red sores & fin/tail/mouth rot

You see: open crater-like sores, raised or missing scales, ragged or receding fins, red streaks in the fins or body.

Likely cause: Aeromonas / Pseudomonas bacteria, almost always following stress or an injury.

Reach for KoiCure Tricide-Neo dip Elbagin MelaFix
Fungus
Cotton-like, fuzzy grey/white growth

You see: cottony tufts on skin, fins or an old wound, often where scales were lost or a parasite bit.

Likely cause: a fungal infection (Saprolegnia), typically secondary to injury or poor water.

Reach for PimaFix ProForm-C Povidone iodine
Parasites · visible
Fish lice & anchor worm you can see

You see: flat, disc-shaped lice moving on the body, or whitish thread-like anchor worms sticking out of a red, inflamed spot.

Likely cause: crustacean parasites: Argulus (fish lice) and Lernaea (anchor worm).

Reach for ProForm-LA
Wound care & handling
Open wounds, lost scales & healing

You see: a healing ulcer, a graze or missing scales after netting, or a fish you need to hold still to treat or inspect.

Reach for: a topical sealant to protect the wound, a slime-coat aid to reduce stress, plus a koi-safe sedative for hands-on work.

Reach for Debride ointment Debride ProHealth SedateSafe

A note on the serious ones: koi showing "pinecone" raised scales (dropsy) or advancing internal infection usually need injectable antibiotics prescribed by a fish vet, and dropsy in particular carries a poor prognosis once the scales lift. When in doubt, quarantine the fish, keep the water pristine, and call us or a qualified koi vet before dosing.

How to treat koi safely

A quick ingredient guide and the ground rules that keep treatments working and fish safe.

Swipe the table to see the cautions →

Active ingredientTreatsGood to know
Malachite green + formalin Ich, costia, trichodina, chilodonella, velvet & fungus The broad first-line parasite/fungus treatment. Don't run it alongside salt. Aerate hard, and use the lower dose on scaleless/doitsu koi.
Praziquantel Gill & skin flukes, tapeworms Very gentle on fish and the biofilter. The go-to for flukes; often used spring and fall as a reset.
Flubendazole Gill & skin flukes Long-acting and effective at all temperatures. A strong alternative to praziquantel, especially for stubborn gill flukes.
Oxolinic acid / nitrofuran antibiotics Bacterial ulcers, fin rot, septicemia Work best as medicated food while koi are still eating. Fix water quality first or the infection returns.
Tris-EDTA + neomycin (dip) Surface ulcers, fin/tail/mouth rot A short every-other-day dip. Treats external sores only; deep infection also needs medicated food. Don't reuse the solution between fish.
Diflubenzuron (ProForm-LA) Fish lice & anchor worm Three doses a week apart to catch newly hatched parasites. Safe for scaleless koi, snails and plants at label dose.
Tea-tree / bay botanicals (MelaFix, PimaFix) Mild fin damage, minor wounds, fungus Gentle, filter-safe support for mild cases and new-fish care, but not a replacement for antibiotics in advanced disease.
Aquarium salt Stress relief, mild parasites, wound support A useful all-rounder, but don't combine it with malachite-green/formalin treatments.

Dose by pond volume

Know your true gallons and measure carefully. Under-dosing wastes the treatment; over-dosing can harm the fish.

Aerate hard, turn off UV & carbon

Most treatments lower oxygen, so add an air stone. Carbon and UV strip meds out of the water, so bypass them while treating.

One treatment at a time

Don't stack medications hoping for a faster cure. Some combinations are toxic (salt with malachite/formalin) and layering antibiotics stresses fish and the filter.

Quarantine new & sick koi

A separate tank lets you treat one fish precisely, keep the disease out of the main pond, and observe new arrivals before they join the collection.

Common questions

Where do I start if my koi looks sick?＋
Test your water first: ammonia, nitrite, nitrate, pH and temperature. Bad water is behind most "diseases," and no medication fixes it. If the water is clean, match what you can see to a symptom card above, and when in doubt move the fish to a quarantine tank so you can treat it precisely.
How do I know if it's parasites or bacteria?＋
As a rule of thumb: itching behaviour (flashing, rubbing, clamped fins, excess slime) points to parasites, while open sores, ragged fins and red streaks point to a bacterial infection. Parasites and bacteria often go together, since a parasite bite is the wound bacteria move into. A cheap microscope and a skin-scrape is the only way to be certain, and it's the best upgrade a serious keeper can make.
Can I just add salt?＋
Pond salt is a great general tonic: it relieves stress, helps with some parasites, and supports fish carrying wounds. But it isn't a cure-all: it won't clear flukes or an established bacterial ulcer, and importantly you should not run salt at the same time as malachite-green/formalin parasite treatments. Use it as support, not as your only tool.
Do these treatments harm my biological filter?＋
Most of the treatments we stock are chosen to be gentle on the biofilter at label dose, praziquantel, flubendazole and the botanicals in particular. Some strong oxidisers and antibiotics can knock back beneficial bacteria, so watch your ammonia and nitrite during and after treatment and be ready with water changes. Always follow the dosing and water-change directions on the bottle.
How much medication do I need?＋
Everything is dosed by water volume, so start from your real pond gallons. Each product page lists exactly how many gallons a bottle or jar treats and how many rounds a course takes, so you can buy the right size the first time. If you're between sizes, size up. Treatments have a shelf life and you'll likely want it again in spring and fall.
When should I call a vet instead of dosing?＋
Call a qualified koi vet for a valuable fish that is badly ulcerated, showing "pinecone" raised scales (dropsy), or not responding to treatment. Deep and systemic infections often need injectable antibiotics that only a vet can prescribe and administer, and getting the right drug from a lab culture beats guessing. We're always happy to talk it through first. Reach us before you dose if you're unsure.
Talk to our koi team