Quarantine and treating a sick fish

Short answer: most fish disease is best handled in a separate quarantine tank, not your main display. Quarantine every new fish for a few weeks before it joins your others, and move a sick fish out to treat it. The two problems you will meet most often are ich (white spots, from a parasite) and fin rot (ragged, receding fins, usually from poor water quality). Many mild cases improve with clean, stable water and warmth alone. When a medication is needed, follow the label exactly for dose, species and duration — and if you are unsure, ask us or your vet before treating. We would rather advise than guess.

Why quarantine matters

New fish can carry parasites or bacteria that do not show up for days or weeks, and adding them straight to an established tank risks the whole community. A simple quarantine tank — a bare tank with a heater, a mature sponge filter and somewhere to hide — lets you watch new arrivals, and treat them if needed, without medicating your display or exposing your other fish. It doubles as a hospital tank when something goes wrong.

• Keep it simple: a small tank, a heater holding a steady temperature, and a sponge filter you can move over from an established tank so it is already biologically active.
• Quarantine new fish for about two to four weeks and watch for spots, ragged fins, laboured breathing or unusual behaviour.
• Keep the water pristine with regular changes — clean water is itself a treatment.

Common problems to recognise

• Ich (white spot). Small white grains like salt scattered over the body and fins, often with flicking against surfaces. It is a parasite with a temperature-driven life cycle, so treatment usually runs over a period of days rather than a single dose.
• Fin rot. Fins that look ragged, milky or are receding, often edged in red. It is usually secondary to stress or poor water quality, so correcting the water is half the cure.
• Fungus, velvet and others. Cottony growths, a fine gold dusting, or rapid breathing all point to different causes. If you are not sure what you are looking at, send us a clear photo before treating.

A test kit helps you catch the water-quality problems behind many of these before they start — browse test kits.

Treating safely — the honest part

This is where care matters most. We will not tell you a specific medication is safe for your particular fish, because it depends on the product, the species and the situation. Instead:

• The label is the authority. Read it in full and follow the dose, timing and species guidance exactly. Never assume more is better, and never mix treatments unless the label says you can.
• Scaleless fish and invertebrates are sensitive. Loaches, many catfish, shrimp and snails react badly to a number of common medications, especially anything with copper. If your tank holds any of these, confirm from the label that the product is safe for them first — our guide on shrimp-safe medications explains why.
• Diagnose before you dose. Do not medicate “just in case.” Identify the problem first, treat in the quarantine tank, and remove any activated carbon while medicating as it strips out many treatments.
• When in doubt, ask. Bring us the details or a photo, or speak to an aquatic vet. A wrong treatment can do more harm than the disease.

You will find treatments and conditioners in our medications range, and aquarium salt, which some keepers use as a mild supportive treatment for certain fish — again, follow the guidance for your species and never use it blind.

Prevention beats treatment

Most disease traces back to stress and unstable water, so the best medicine is a well-cycled, well-maintained tank. If you are still setting up, how to cycle a new aquarium covers the foundation that keeps fish healthy in the first place.

Written by the team at Tropical Fish Imports in Lethbridge, Alberta. Last reviewed August 2026.

Not sure what you are dealing with, or which treatment is right? Please ask before you dose — bring a photo or the details into the shop, call 403-380-4506, or send us an email, and we will help you work it out.