Aquarium Rescue · Symptom Checker
Fish Symptoms Checker
Not sure what’s wrong? Tap the symptom you’re seeing and get the most likely causes, the safe first steps to take now, and a direct link to the right rescue guide. Calm, beginner-friendly, no guesswork.
Start here
What are you seeing?
Tap a symptom. When in doubt, the safest first move is always to test your water and add gentle aeration — not to add chemicals.
This tool offers general educational guidance, not veterinary advice, and makes no guarantees. Seeing several symptoms at once usually points to a water-quality problem — start by testing your water.
First 5 minutes
Emergency Actions for (Almost) Any Symptom
Note which fish, which symptoms, and anything that changed in the last 48 hours.
Ammonia, nitrite, pH and temperature — the fastest way to find an invisible cause.
An air stone, or aim the filter outflow at the surface, to raise oxygen.
25–50% with dechlorinated, temperature-matched water if ammonia or nitrite shows up.
Take out uneaten food, dead fish and decaying plants; hold off feeding while you stabilise.
Avoid these
What NOT To Do
- Don't pour in random chemicals or "cures" before testing — a water change is usually the safest first action.
- Don't do a 100% water change — it crashes the good bacteria keeping the tank safe.
- Don't shotgun multiple medications at once.
- Don't shock-cool a warm tank with ice — change temperature slowly.
- Don't keep feeding a fish that won't eat — uneaten food rots into ammonia.
- Don't restock to replace losses until the tank is stable again.
Good questions
Symptom Checker FAQ
Can I diagnose my fish from symptoms alone?
Symptoms narrow it down, but they rarely confirm the cause on their own — most point back to water quality or oxygen. Use this checker to find the likely problem, then test your water to confirm before acting.
My fish has several of these symptoms — what now?
Multiple symptoms at once almost always mean a water-quality issue. Test ammonia, nitrite, pH and temperature first, add aeration, and start with the Aquarium Rescue Hub.
Are these symptoms always serious?
Not always — a fish resting on the bottom can be normal for some species. It's the sudden changes, and several signs together, that mean you should act.
What should I check first for almost any symptom?
Your water. Ammonia and nitrite (both should read 0), temperature, and oxygen are behind the large majority of fish problems. A liquid test kit is the single most useful tool you can own.
Is this a substitute for a vet?
No. This is educational guidance to help you act quickly and safely. For a serious or persistent illness, consult a qualified aquatic vet or a trusted local fish store.
Found your symptom? Get the full rescue plan.
Each symptom links to a step-by-step rescue guide. Grab the free checklist to catch the next problem early.