Ich and bacterial infections can both make fish look unwell, but they need completely different treatments. Ich is a parasite, so antibiotics do nothing against it. Here’s how to tell them apart before you buy anything.
What ich looks like
Ich, or white spot disease, is caused by the parasite Ichthyophthirius multifiliis. It shows as small, even white spots, like grains of salt or sugar, on the body, fins and gills. Fish often rub against objects (“flashing”), clamp their fins and breathe faster.
What bacterial infections look like
- Ragged, receding fins with white or red edges (fin rot).
- Red streaks, sores or open ulcers.
- Grey-white patches on the back or mouth (columnaris).
- Cloudy eyes, or a swollen body with raised scales (dropsy).
Side by side
| Ich (parasite) | Bacterial infection | Fungus | |
|---|---|---|---|
| Spots | Even, pinpoint white spots like salt | No spots: patches, sores or frayed edges | Fluffy tufts, usually on a wound |
| Rubbing (flashing) | Common | Less common | Uncommon |
| Spread | Many fish within days | Varies | Usually one injured fish |
| Treated with | A medicine labeled for ich | An antibiotic labeled for the signs | An antifungal |
Other look-alikes
- Velvet, another parasite, looks like a fine gold or rust-colored dust rather than distinct white spots.
- Lymphocystis, a virus, causes lumpy, cauliflower-like growths. Neither antibiotics nor antifungals treat it.
- Breeding tubercles on male goldfish are small white bumps on the gill covers and front fins in breeding season. They are normal.
If it’s ich
Use a medicine labeled for ich and follow its directions. Treat the whole tank, because the parasite spends part of its life in the water rather than on the fish. The antibiotics and antifungals in our range will not treat ich.
If it’s bacterial
Test the water, move the fish to a hospital tank and choose a product labeled for the signs you see. Our guide How to choose an aquarium antibiotic matches signs to labels. The Merck Veterinary Manual notes that most bacterial pathogens of fish are gram-negative (Bacterial Diseases of Fish).
When you can’t tell
Take a clear, close photo in good light and compare it with the table. If you’re still unsure, an aquatic veterinarian can look at a skin scraping under a microscope, which shows parasites such as ich directly.
Browse all fish antibiotics, compared by ingredient, strength and count.
Fish antibiotics are for ornamental aquarium fish only: not for human use and not for food-producing animals. This guide is general information, not veterinary advice; for valuable or persistently sick fish, ask an aquatic veterinarian. Last reviewed: November 2026.