What's Wrong With My Fish? Start Here
Your fish is acting strange and you need answers now. FishSymptoms is a symptom-first help site for freshwater aquarium keepers: pick what you can see, get ranked likely causes, and do the right first thing — usually a water change and a test, not a mystery bottle from the pet shop.
Last updated: November 2026
Act now if you see these
- Gasping at the surface or all fish huddling near the outflow — possible low oxygen or ammonia spike. Emergency steps →
- Floating at the top but not dead — a passive floater is poisoning or oxygen, not sleeping. First-hour rescue →
- Tank under 6 weeks old + any distress — assume ammonia/nitrite poisoning until a liquid test says otherwise. New tank help →
- Red streaks, sores, or rapid deterioration — likely bacterial septicemia; water changes today matter more than any medication. What to do →
Severe cases: consult an aquatic-experienced vet where available.
Find my problem
Symptom Finder
Tick what you see, add tank context, get ranked causes plus first actions.
Stocking Calculator
Is your tank overstocked? Surface-area and rule-of-thumb estimates.
Best Test Kit
Liquid vs strips, what to buy first, and the numbers that are safe.
Common symptoms
Gasping at the surface
Low oxygen, ammonia, gill disease — first hour protocol.
Floating at top, not dead
Is it dead or sleeping? The check, the decision table, the rescue.
White spots (that may not be ich)
Ich vs costia vs lymphocystis comparison table.
Lying on the bottom
Stress, temperature, swim bladder, or organ failure.
Floating upside down
Swim bladder first aid, especially in goldfish.
Not eating
A decision tree from "just stressed" to "sick enough to isolate".
Red streaks & sores
Columnaris, septicemia, ulcers — act fast.
Cloudy water
New-tank bacteria vs crashes vs overfeeding.
Green water
How to crash a bloom in days, then keep it down.
Common symptoms A–Z
Every symptom guide on the site, alphabetical — or start with the Symptom Finder and let it rank causes for your exact fish.
Cloudy water
New-tank bacteria vs crashes vs overfeeding.
Fish dying in a new tank
New tank syndrome, the cycle timeline, the rescue.
Floating at top, not dead
Dead-or-alive check and first-hour rescue.
Gasping at the surface
Emergency protocol for low oxygen and poisoning.
Green algae bloom
Crash the bloom in days, then keep it down.
Lethargic, not eating
Bottom-sitting triage: test water before treating.
Lying on the bottom
Nap, cold stress, poisoning, or dropsy.
Noisy tank filter
Why the filter roared back — and the fixes.
Not eating
Decision tree from "just stressed" to "isolate".
Red streaks & sores
Columnaris, septicemia, ulcers — act fast.
Swimming sideways / upside down
Swim bladder first aid and balance-loss causes.
White spots
Ich vs costia vs velvet vs lymphocystis.
Species care profiles
Betta
Heated 5+ gal, labyrinth breathing, fin rot watch.
Goldfish
Cold water, heavy waste, swim bladder issues.
Neon tetra
Schools of 6+, neon tetra disease explained.
Guppy
Hardy but prone to ich and flukes in cold dips.
Angelfish
Tall tanks, warm water, temperament notes.
Corydoras
Bottom crew, smooth substrate, barbel care.
Can fish eat it?
Quick verdicts on the human foods people actually ask about:
Bread
No. Swells, fouls water, no nutrition.
Peas
Yes — shelled and blanched. Classic constipation fix.
Rice
Only cooked, tiny amounts. Uncooked is dangerous.
Grapes
No. Sugar, pesticides, choking size.
Watermelon
Yes — rind and flesh, seedless, small pieces.
Cheese
No. Fish cannot digest dairy fat or lactose.
Human food (all)
The umbrella verdict: plain veg yes, seasoned food no.
Browse all fish food safety guides →
Browse everything on FishSymptoms
Emergencies & first aid
Species care guides
Tools & gear
Can fish eat it? — all verdicts
Free: New Tank Cycle Checklist (PDF)
The day-by-day checklist we wish every beginner had before adding fish: target ammonia/nitrite/nitrate numbers, when to test, and when the tank is actually safe.
Or download the checklist PDF now — no email needed.
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