White salt-like spots are usually ich, gold dust is velvet, and frayed fins are fin rot. Each disease with its signs and treatment below.
Signs: Salt-like white dots on body and fins; the fish scratches on objects.
Usual treatment: Formalin 25 mg/L (about 1 mL per 38 L) daily, 3–5 treatments at 24–26°C, or copper by alkalinity (alkalinity ÷ 100 = mg/L), or salt 4–5 g/L for 7–10 days for tolerant species. Vacuum the bottom every two days for the cysts. Source: University of Florida FA006 · Confirm the dose with a vet.
Signs: Gold or rust dust on the body (clearer with a torch), clamped fins and fast breathing.
Usual treatment: Isolate and darken; in a hospital tank treat with copper (by alkalinity) or chloroquine 10 mg/L as a prolonged bath (non-food fish), repeating to break the life cycle. Source: Merck · Confirm the dose with a vet.
Signs: Fin edges eaten away with white or red margins.
Usual treatment: Fix the cause first (ammonia, nitrite, crowding or nipping). Antibiotics only if fish are dying: kanamycin 50–100 mg/L as a 5-hour bath every 3 days for 3 treatments, with a water change after each bath. Source: Merck · Confirm the dose with a vet.
Signs: White-grey cotton patches on the mouth or back (saddle); spreads fast.
Usual treatment: Early diagnosis matters. Potassium permanganate 2 mg/L helps early, salt 1 g/L lowered deaths in studies; then usually a medicated feed chosen by a vet. Source: PMC3648355 · Confirm the dose with a vet.
Signs: Soft cotton tufts on wounds or on eggs.
Usual treatment: Remove the cause first (right temperature, hygiene, remove dead fish and eggs). Potassium permanganate 10 mg/L for 10 minutes in a tank (or 2 mg/L in a pond); wait at least 4 days before repeating. Source: Texas A&M · Confirm the dose with a vet.
Signs: Swollen belly with scales standing out like a pinecone.
Usual treatment: Isolate at once. Treat the cause: if bacterial, the antibiotic is chosen by a vet after a sensitivity test (in feed or injected). Outlook is poor, so protect the rest of the tank and the water. Source: Merck · Confirm the dose with a vet.
Signs: The fish floats, sinks or swims tilted.
Usual treatment: Fast for 2–3 days, keep the temperature steady, improve the water, then a sinking easy food. See a vet if it does not improve. Source: Zajel medical library (published study) · Confirm the dose with a vet.
Signs: Small pits in the head (discus and cichlids) and white stringy poop.
Usual treatment: Metronidazole in food 50 mg/kg (or 10 mg per gram of food) for 5 days, or a 5 mg/L bath daily for 5 days with a 70–100% water change before each dose. Clean gravel and filter. Source: University of Florida · Confirm the dose with a vet.
Signs: Scratching, gasping, gills flared or red.
Usual treatment: Praziquantel prolonged bath 2–5 mg/L for 2–3 weeks; for egg-laying gill flukes repeat every 1–4 weeks (3 courses). Alternative: formalin 30 mg/L. Source: University of Florida FA033 · Confirm the dose with a vet.
Signs: White dots on marine fish, scratching and fast breathing.
Usual treatment: Hospital tank only: ionic copper 0.15–0.20 mg/L (test twice daily) for 3–6 weeks, or chloroquine 10 mg/L prolonged bath, or formalin 25 mg/L with salinity 16–18 g/L every other day for 4 weeks. Cysts can release parasites for up to 72 days; quarantine 30–90 days. Source: University of Florida FA164 · Confirm the dose with a vet.
Signs: Small red worms out of the vent and wasting; common in guppies.
Usual treatment: Fenbendazole in food 25 mg/kg for 3–5 days, or a levamisole bath 2 mg/L; vacuum the substrate well. Source: Merck · Confirm the dose with a vet.
Signs: Colour fades from inside out, the spine bends, the fish stays alone.
Usual treatment: No cure. Remove affected fish at once so it does not spread, and euthanize humanely if it suffers. Source: Merck
Signs: White-pink cauliflower lumps on fins or body.
Usual treatment: Viral with no medicine; it usually clears by itself. Improve water and reduce stress. Source: Merck
Signs: A guppy or molly shimmies in place with clamped fins, usually from soft or cold water or ammonia.
Usual treatment: No firm veterinary reference (low confidence): fix the water first (ammonia, nitrite, temperature, hardness) and treat any parasite confirmed by examination.
Signs: Slow wasting, bent spine, ulcers and faded colour, one death after another over weeks.
Usual treatment: No effective cure in fish: isolate and remove affected fish humanely. ⚠️ It can infect people: wear gloves if your hands have cuts and never start a siphon by mouth. Source: Merck
Signs: Red gills, gasping at the surface, usually in a new tank or after overfeeding.
Usual treatment: Reduce or stop feeding for 1–3 days (except fry), change 25–50% with ammonia-free water and test daily until it reads zero. Source: Merck
Signs: Fine dust on the body and very fast breathing; kills within days.
Usual treatment: Dangerous and fast. In a hospital tank: chloroquine 10 mg/L prolonged bath, or ionic copper 0.18–0.2 mg/L for up to 3 weeks with daily testing. Source: Merck · Confirm the dose with a vet.
Signs: Peeling skin and heavy slime, mostly in new clownfish.
Usual treatment: Formalin 15–25 mg/L prolonged bath (25 mg/L = about 1 mL per 38 L); ionic copper is also listed by Merck for marine fish. Source: Merck · Confirm the dose with a vet.
Signs: Open red ulcers that grow fast.
Usual treatment: If only external: formalin or copper with better hygiene. Once it invades tissue treatment is hard, so see a vet. Source: Merck · Confirm the dose with a vet.
Signs: Erosion around the head and lateral line, mostly in tangs.
Usual treatment: Not contagious. Fix the environment and diet (variety, algae). The University of Florida notes a possible link with ozone by-products; the cause is still unsettled. Source: University of Florida
Doses differ by brand: always follow the label, and ask a fish vet for valuable fish or late cases.
