Health

How to treat ich (white spot disease): symptoms and treatment

By The FishFits team · Updated

To treat ich, dose the whole tank with an ich medication (usually malachite green, formalin plus malachite green, or copper) exactly as the label says, remove carbon from the filter, add aeration, and keep treating until at least 3 days after the last white spot is gone. If every animal in the tank can take it, raising the temperature slowly to the top of their range (never above about 86 °F / 30 °C) speeds up the parasite's life cycle, and aquarium salt at 2–3 g per liter (about 7.5–11 g per gallon) helps salt-tolerant fish such as livebearers and goldfish. Keep copper away from shrimp and snails, keep salt away from snails, live plants, loaches and most catfish, and quarantine new fish for at least 30 days so ich doesn't come back.

Ich (Ichthyophthirius multifiliis), or white spot disease, is one of the most common parasites of freshwater aquarium fish, and it is very treatable when caught early. The key fact: medication can’t reach the white spots. It works only after the parasite leaves the fish, mainly on the free-swimming young, so you treat the whole tank, repeatedly, until every parasite has passed through that stage.

This guide covers common, well-established home treatments. It doesn’t replace an aquatic vet, and your product’s label always comes first.

How to tell if it’s ich

The classic sign is raised white dots like grains of salt on the body and fins, more each day. Each dot is usually one parasite, up to about 1 mm (0.04 in) across.

Other signs, often before the spots appear:

  • Flashing: fish dart and rub their sides on gravel, rocks or decor.
  • Fast breathing, or hanging near the surface or filter outflow.
  • Clamped fins, hiding, sluggishness and refusing food.
  • Extra slime, which can make the skin look cloudy or bumpy.

Ich can also stay on the gills only, causing fast breathing and sudden deaths with few or no spots. White spots alone don’t prove it’s ich; a vet confirms it by finding the parasite in a skin or gill sample.

Looks like ich, but… How to tell the difference
Velvet Much finer gold or rust-colored “dust”, easiest to see with a flashlight
Breeding tubercles on male goldfish White bumps only on the gill covers and first pectoral fin rays, in a neat pattern, that don’t spread
Fungus Cottony, fluffy tufts, often on a wound
Lymphocystis Lumpy, cauliflower-like growths that grow slowly over weeks

The ich life cycle and why it matters

Stage Where it is Can medication reach it?
Trophont (the white spot) Under the fish’s skin, feeding No, the skin shields it
Tomont (cyst) Drops off and sticks to glass, gravel, plants or decor, then divides inside a cyst Mostly no, the cyst protects it
Theront (swarmer) Bursts from the cyst and swims off to find a fish Yes, this is the stage treatments kill

Each cyst releases hundreds of swarmers, sometimes up to about 2,000. A swarmer that finds no fish within a day or two usually dies, so ich can’t last long in a fishless tank.

Temperature sets the pace. At 75–79 °F (24–26 °C) the full cycle takes about 3–6 days; below 45 °F (7 °C) it can take more than 5 weeks. Ich usually can’t reproduce properly above about 85 °F (30 °C), although one outbreak killed fish at 92 °F (33 °C).

So a single dose never works, and spots can look the same or worse for the first 2–3 days while parasites already under the skin finish growing and drop off.

How to treat ich step by step

  1. Confirm it’s ich. If you aren’t sure, ask a vet before you medicate.
  2. Test the water. Ammonia and nitrite should be 0 ppm. Do a 25–30% water change and vacuum the gravel to pull out cysts (see the water changes guide).
  3. Check for shrimp, snails and plants. The most sensitive animal decides the method. Move shrimp and snails to a heated, fish-free tub unless your medication is labeled safe for them.
  4. Prepare the filter. Remove carbon and chemical pads, which absorb medication, and switch off any UV sterilizer. Keep biological media running.
  5. Use the real water volume. Substrate and decor take up space; the aquarium volume calculator gives a better number to dose against.
  6. Dose the whole tank at the label rate and add an air stone, because some medications, especially formalin, use up oxygen. Wear gloves and keep medication off your skin.
  7. Raise the temperature slowly if every species can take it and your label allows it, by about 1–2 °F (0.5–1 °C) a day (limits below).
  8. Repeat on the label’s schedule, usually every 24 or 48 hours. Some labels also ask for a 20–25% water change and gravel vacuum before each full-tank dose.
  9. Feed lightly and test ammonia daily.
  10. Keep going for at least 3 days after the last spot is gone, or longer if the label says.
  11. Finish up. Do a 30–40% water change, add fresh carbon to pull out leftover medication, and lower the heat 1–2 °F (0.5–1 °C) a day.

No improvement at all after about 5 days of correct dosing? The diagnosis may be wrong, so talk to a vet before switching or adding products.

Which treatment suits your tank

Your tank Best first choice Avoid
Tropical community fish Medication, plus mild heat within everyone’s range Heat past the least tolerant fish’s range
Corydoras, plecos, otocinclus or loaches Medication, following any label note on scaleless fish Salt; copper unless the label clears it
Shrimp or snails Move them out, or treat all fish in a hospital tank Copper, salt, products not labeled invertebrate-safe
Heavily planted Medication labeled plant-safe Salt and copper, which can harm plants
Goldfish Salt or medication Heating well above their coldwater range, which tops out around 72–73 °F (22–23 °C) in our data
Warm-water fish (discus, German blue rams, clown loaches) Medication, plus heat to 84–86 °F (29–30 °C) with strong aeration Letting the temperature drop or swing

Loaches and catfish. Loaches have very small scales, and corydoras, plecos and otocinclus have bony plates instead, so labels often group them as “scaleless”. Labels disagree: at least one popular remedy calls for half the dose for some scaleless fish, while other makers and sellers say full strength is safe and a weaker dose may not work. Follow your own bottle, keep lights dim and aerate well. Clown loaches are especially prone to ich when stressed or kept too cool.

Treating the fish elsewhere. If the display has many shrimp, snails or plants, treat all the fish in a bare hospital tank. With no fish to infect, ich in the display dies off. Keep it fish-free and heated for at least 7 days (10–14 days gives a margin), and return the fish once their treatment is finished.

Ich medications by active ingredient

Product names vary by country, so check the active ingredient, and never combine medications unless both labels say it is safe.

Active ingredient Strengths Main cautions
Malachite green Kills swarmers; some products are sold as safe for plants, shrimp and snails Can stain ornaments, artificial plants and silicone; carbon removes it; elephantnose fish are very sensitive
Formalin plus malachite green Widely used two-in-one Formalin uses up oxygen, so aerate hard and add heat only if oxygen is assured; one major label rules out invertebrates and warns elephantnose fish and freshwater stingrays may react badly
Copper (chelated or copper sulfate) Effective in fish-only and hospital tanks Toxic to snails, shrimp and most invertebrates; can harm plants; more toxic to fish in soft, low-alkalinity water, and an overdose kills fish; a copper test kit is advised
Aquarium salt (sodium chloride) Simple option for salt-tolerant fish Harms most plants and snails; catfish and loaches are more sensitive; some ich strains have survived 3–5 g/L
Potassium permanganate Used in ponds and fish farms Easy to overdose, and repeated use damages skin, gills and eyes; leave it to vets and pond specialists

Don’t cut the dose “to be gentle” unless the label says to for your species; a weak dose may not kill ich. Don’t add extra “for good measure” either, which can kill fish.

Using heat, and its limits

Warmer water speeds up the life cycle, so swarmers meet the medication sooner. But many popular fish can’t live near 85 °F (30 °C) and some ich survives hotter water, so heat is a helper, not a cure. Warm water also holds less oxygen, which matters most with formalin, so keep an air stone running and watch for gasping.

Raise the heater only to the top of the least tolerant animal’s range. Tops of the ranges in FishFits’ species data:

Species Top of range
Discus, German blue ram, clown loach 86 °F (30 °C)
Angelfish 84 °F (29 °C)
Cardinal tetra, betta, dwarf gourami, sterbai corydoras 82 °F (28 °C)
Guppy, molly, kuhli loach 81 °F (27 °C)
Bronze corydoras, bristlenose pleco, otocinclus 79 °F (26 °C)
Neon tetra, panda corydoras 77 °F (25 °C)
White cloud mountain minnow 72 °F (22 °C)

So neon tetras and panda corydoras stay at 77 °F (25 °C) or below and rely on medication, while a clown loach tank can go to 86 °F. For a mixed tank, the compatibility checker shows the shared range, and the tank temperature guide covers more species.

Using aquarium salt

Plain aquarium salt (sodium chloride) works because swarmers don’t tolerate raised salinity. Use it only with salt-tolerant fish such as livebearers, goldfish, most cichlids, danios and many tetras, and never use table, marine or Epsom salt.

Actual water volume 2 g/L (start here) 3 g/L (tolerant fish only)
5 gallons (19 L) 38 g (1.3 oz) 57 g (2.0 oz)
10 gallons (38 L) 76 g (2.7 oz) 114 g (4.0 oz)
20 gallons (76 L) 151 g (5.3 oz) 227 g (8.0 oz)
55 gallons (208 L) 416 g (14.7 oz) 625 g (22.0 oz)

Weigh it if you can: the hobby measure of 1 level tablespoon per 2 gallons is roughly 2–2.5 g/L, but crystal size changes how much a spoon holds.

  1. Dissolve the salt in a jug of tank water and add it in two or three portions over 12–24 hours.
  2. Keep it in for about 10 days, and at least 3 days after the last spot is gone.
  3. Salt doesn’t evaporate, so top up with plain dechlorinated water and add salt back only for water you change (25% of 20 gallons at 2 g/L needs about 38 g).
  4. Afterwards, remove it with plain-water changes over 1–2 weeks.

If spots still spread after about 5 days on salt, switch to a medication rather than raising the salt on your own.

When to see an aquatic vet

Call an aquatic or exotic-animal vet if fish are dying quickly, gasping with few or no spots (possible gill ich), not improving after about 5 days of correct treatment, or you aren’t sure it’s ich. A vet can confirm the diagnosis and prescribe treatments not sold in stores. Damaged skin lets bacteria in, so watch for ragged fins or red sores afterwards (see the fin rot guide); the fish dying guide helps rule out water problems.

How to keep ich out

Ich arrives with new fish, plants, decor or wet equipment, or survives at low levels on fish from an earlier outbreak and flares up after stress or a fast temperature change.

  1. Quarantine new fish for at least 30 days in a separate tank with a heater, a seeded sponge filter and a bare bottom. Restart the clock if any disease appears.
  2. Never pour store water into your tank. Net the fish out of the bag, as the fish acclimation guide explains.
  3. Quarantine plants too. Keep them in a fish-free container for at least a week at tropical temperatures (longer if cooler) so any cysts hatch and die.
  4. Use separate nets, siphons and buckets for each tank, and dry them fully between uses. Keep tanks covered, because ich can travel in water spray between nearby tanks.
  5. Keep conditions steady. Well-fed fish in clean, stable, uncrowded water resist ich far better than stressed fish.

Gear mentioned in this guide

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Frequently asked questions

How long does it take to get rid of ich?

Plan on at least a week, and often longer. Treatment has to cover several turns of the life cycle and then carry on for at least 3 days after the last spot; one cycle takes under a week in a tropical tank and much longer in cool water. One major medication label says daily dosing can take anywhere from 6 to 35 days or more.

Do I need to treat the whole tank or just the sick fish?

Treat the whole tank. By the time you see spots, cysts are already on the gravel and decor and free-swimming parasites are in the water, so every fish has been exposed. Moving only the spotted fish leaves the outbreak running in the main tank.

Is ich medication safe for shrimp and snails?

Not always. Copper is toxic to shrimp and snails, salt is unsuitable for most snails, and some ich medications are labeled not for invertebrates, although some malachite green products are sold as shrimp- and snail-safe. The safest route is to move shrimp and snails to a heated, fish-free tank during treatment; ich can't live without fish, so after at least a week apart (two weeks gives a margin) any parasites riding with them will have died.

Can ich go away on its own?

Rarely in an aquarium. Each cyst that drops off a fish releases hundreds, and sometimes up to about 2,000, new parasites into a small volume of water, so an untreated outbreak usually grows fast. Fish that survive can carry low levels of ich without showing spots and pass it to new fish.

Can humans catch ich from fish?

No. Ich only infects fish and poses no risk to people. Still wash your hands and forearms after working in the tank, and keep separate nets and siphons for each tank, because wet equipment can carry ich to your other fish.

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