White spots on a goldfish

White spots are one of the most searched goldfish symptoms, and one of the most misread. The classic case is ich — often spelt ick, and properly Ichthyophthirius multifiliis — a parasite that shows up as a dusting of salt-like grains across the body and fins. But some common “white spots” are perfectly healthy: the breeding tubercles of a male in spring, or new growth on the hood of an oranda. The difference is usually obvious once you know where to look and how the fish is behaving.

Telling the causes apart

Ich spots are scattered and untidy. They appear on the body, the fins and often the gill covers, and their number grows over a day or two. The fish usually shows other signs of irritation: rubbing on decor, clamped fins, faster breathing. Everything about it says “something is wrong”.

Breeding tubercles are the opposite. They are small, evenly spaced and usually confined to the gill plates and the leading edge of the pectoral fins. The fish is bright, active and often chasing tankmates. Nothing spreads. If you see this on an otherwise lively fish in spring, you have a mature male, not a patient.

Where the difference shows

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Photograph: Yatokin, CC BY-SA 4.0 · Wikimedia Commons. Numbers and lines added.

1. Gill covers. Small, hard, white tubercles: the clearest external sign of a male in breeding condition, when it is there.
2. Pectoral fins. The same tubercles, in a row along the leading ray. Together with the gill covers, a neat pattern on a well fish usually means a male, not white spot.
3. Vent. Just in front of the anal fin. In condition, a male’s is small, narrow and slightly concave, a female’s rounder and slightly protruding.
4. Belly. Not a reliable sign. A full outline can be eggs in condition; out of season it can be a well-fed fish, but fluid and illness swell the belly too, so a swollen fish with raised scales or lethargy needs a vet.

New growth on a wen is the same kind of false alarm, and is confined to the head hood on an oranda, ranchu or lionhead — wen care covers what the tissue is doing as it develops.

Cotton-like tufts, larger irregular patches, or a single slow-growing lump are not ich either, and treating them with an ich product will not help.

A quick test before any of that: do the spots move with the fish? Mineral deposits and marks on the glass line up with a fish convincingly from one angle and separate the moment you move your head. It sounds too obvious to mention and it saves a certain number of people a bottle of medication. So does looking twice at spots that are clear and glinting rather than white: those are bubbles, usually after a water change.

What to do first

Test the water. Ammonia and nitrite readings above zero suppress the immune response and make any treatment much less likely to work. If either is present, a partial water change is the first action, before any medication.

Check the temperature and think about the last two weeks. A drop of a few degrees, a new fish added without quarantine, or plants from a shop tank are the usual routes in. Knowing the trigger helps you prevent a repeat.

Then look closely, ideally with a torch against the glass, and decide which of the patterns above you are seeing. If it is ich, treat the whole tank, not just the fish, because most of the parasite’s population is in the water and the substrate rather than on the animal.

Treatment principles

There are two effective approaches: commercial ich treatments, and aquarium salt at a controlled concentration. Warmth is not a treatment on its own, but it shortens the parasite’s cycle, so the salt or the medicine has fewer days to cover, and it has to come with strong aeration. Each has conditions attached. Salt can harm plants and some tankmates. Heat lowers oxygen and needs aeration. Medications have specific dosages that depend on your tank volume, so know your real water volume before you start; the aquarium volume calculator will give it to you.

We do not publish dosages here, because the right amount depends on the product, the volume and the fish. Follow the label of whatever you use exactly, remove activated carbon from the filter during treatment, and keep going for several days past the last visible spot. Using medications safely covers the rest of it — real volume, aeration, what a course does to the filter.

What treatment looks like, day by day

Knowing the shape of it in advance matters, because the course looks like it is failing at exactly the point where most people give up.

Roughly	What you see	What is happening
Days 1–3	Spots the same or increasing	Nothing reaches the parasite under the skin. More of the existing population is maturing into visible spots. This is normal.
Days 3–7	New spots slowing, fish less irritated	The free-swimming generations are being killed as they emerge.
Days 7–14	Spots gone	The last embedded parasites have dropped off and their young have been killed.
Several days past that	Nothing	Keep treating. Any survivor restarts the whole thing.

A common mistake is stopping when the spots disappear. At that moment the fish is clear and the tank is not: encysted parasites on the substrate are still releasing free-swimming young. Continue for several days beyond the last visible spot, and longer in cool water, where every stage of the cycle runs slower.

If new spots are still appearing after a week of correct treatment, that is a genuine signal — check the dose against your real water volume, check that carbon is out of the filter, and consider that you may not be looking at ich.

Temperature, and the advice that is not for goldfish

Worth separating carefully, because this is where goldfish keepers get given tropical-fish instructions.

Why warmth is suggested at all. The parasite is only vulnerable during its brief free-swimming stage. Warmer water speeds the whole cycle, so those vulnerable windows come around faster and the course finishes sooner. At cool goldfish temperatures the same cycle can take two or three times as long, which is why goldfish ich treatment is a longer job than the label suggests.

Why the usual figure is not needed here. The commonly repeated instruction to hold a tank at 30 C comes from tropical fishkeeping. Goldfish are temperate fish; the temperature guide sets out where they should actually sit. Warm water holds less dissolved oxygen at precisely the moment a fish with parasite-damaged gills needs more of it, and a tank held at 30 C needs heavy aeration to stay safe. Heat can turn a treatable infestation into a fish that suffocates.

If you raise it at all: add aeration first, raise by about a degree a day, stop in the low-to-mid twenties Celsius rather than higher, and watch for surface gasping — aeration and oxygen covers how to add more, and gasping at the surface is the sign to stop. Many experienced goldfish keepers skip the heat entirely, accept a longer course, and lose nothing.

Ich in a pond

A different problem with a different answer, and it comes up every spring.

Pond outbreaks typically follow the spring warm-up, when the water rises through the range the parasite likes while the fish are still run down from winter and their immune systems are slow to restart. The cause is often a new fish added the previous season, or the pond’s own resident population taking advantage of stressed hosts.

Treating a pond is harder than treating a tank for the obvious reason: volume. Dosing accurately requires knowing the real volume, which most pond owners have only estimated, and the cost of getting it wrong is proportionally larger. Ultraviolet clarifiers help against the free-swimming stage as water passes through them, but they do not sterilise a pond. In most cases the practical approach is to support the fish — aeration, feeding appropriately for the temperature, and no further additions — and to treat only if the outbreak is progressing. The pond through the year page covers the spring restart, which is the underlying issue.

After the outbreak

The fish being clear is not the same as the tank being clear.

Keep treating past the last spot, as above. Then do a large water change, replace the carbon you removed, and return the filter to its normal routine — but do not clean the filter media during or immediately after a course, because many treatments have already knocked the bacterial colony back and cycling it again is a job you do not need. Test ammonia and nitrite for a week or two afterwards: a treatment that damaged the filter shows up as a small ammonia reading in an established tank.

Equipment that has dried completely is very unlikely to carry live parasites. Nets, siphons and buckets left to dry out are the cheap answer; if in doubt, disinfect them or keep a separate set for the fish that were ill.

A fallow tank clears itself. If the fish can be housed elsewhere — a hospital tank — a tank left fishless runs the parasite out of hosts within a couple of weeks, faster when warm. This is rarely necessary for a single outbreak and is worth knowing about for a recurring one.

Expect the fish to look rough for a while. Damaged slime coat and small skin wounds take time to heal, and a fish that has been through a course of treatment and a parasite load is tired. Clean, stable water and modest feeding do more for that recovery than anything in a bottle. If wounds are opening rather than closing, ulcers and sores is the page for the next stage.

Preventing the next outbreak

Quarantine new fish for at least four weeks, 30 days being the usual veterinary minimum, before they join the main tank. It is tedious and it is an effective step against ich, because the parasite often arrives with a new animal. Keep the temperature stable, keep ammonia and nitrite at zero, and give your fish the water volume and filtration they need. A well-kept goldfish with a strong immune system can shrug off exposure that would overwhelm a stressed one.

Three things worth adding, because fish are not the only route in:

• Plants and equipment can carry it too. Shop plants are usually held in tanks containing fish, so they arrive with whatever those fish had. Quarantining plants is the step nobody takes and it closes a real gap.
• A temperature drop is the usual trigger for an outbreak that was already latent — a winter window left open, a large water change with cold water, a heater that failed. A steady temperature is part of the prevention.
• Do not skip quarantine because the shop looked clean. Ich is invisible for most of its cycle, and a fish that shows nothing on the day of purchase can be carrying it. That is the entire argument for the month.