Fish emergency? Let's find the cause.
Answer a few quick questions and get the most likely reason - and exactly what to do right now. Free, no sign-up, works in your browser.
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Fish deaths, chemistry & water changes
Water colour & clarity clues
Behaviour, breathing & feeding
About Tank SOS
When something goes wrong in a tank it usually goes wrong fast, and forum threads are a slow, contradictory place to be at 2am. Tank SOS asks a few plain questions and lands you on one focused page: the most likely cause, the safest first steps (check oxygen and toxins before reaching for medications), how to stop it happening again, and where to read more. Every answer runs in your browser - nothing is uploaded.
This is triage, not a vet. We can't see your fish, so pair these steps with a liquid test kit and clear photos, and see an aquatic vet or a trusted local shop for a valuable or seriously ill fish.
Frequently asked questions
Fish died overnight - what should I check first?
Run ammonia and nitrite tests if you can. Confirm the filter is running and the surface is moving. Think about anything that changed in the last day or two: water change, new fish, heater, cleaning sprays, or a power cut. Tank SOS walks those branches in order.
Fish gasping at the surface - is it low oxygen or ammonia?
Both can look similar. Test ammonia and nitrite, ripple the surface gently, and confirm the filter output is healthy. Tank SOS splits those paths when you choose behaviour and gasping.
Are white spots on fish always ich?
Discrete salt-sized grains often mean ich (Ichthyophthirius). Fluffy cotton is usually fungal or bacterial. Velvet may look like fine gold dust under a sidelight. Use Tank SOS marks branch and open the ich page linked from there.
What does cloudy aquarium water colour mean?
Grey-white haze in a young tank often follows a bacterial bloom; in an old tank it should trigger an ammonia check. Neon green soup is usually planktonic algae. Brown-yellow tint is commonly tannins or dirty mechanical media. Tank SOS separates these under water appearance.
Why did fish die after a water change?
Typical suspects are untreated chlorine or chloramine from tap water, a big temperature mismatch, or a carbonate hardness swing. Tank SOS asks whether you used dechlorinator and matched temperature before pointing you to fixes.
Can Tank SOS replace an aquatic vet?
No. It offers triage notes for freshwater hobbyists. Sick or valuable fish still need a veterinarian or qualified aquarium professional when unsure.
Does Tank SOS upload my taps to your servers?
No. Questions and answers resolve in your browser using the JSON bundle on this page. Separate site-wide analytics follow our privacy policy.
What setups does Tank SOS cover?
Tropical freshwater home aquarium patterns that mirror our companion guides. It is less reliable for reef marine-only systems or large ornamental ponds without professional follow-up.
Tank SOS isn't veterinary advice - it's a directional read to help you decide your next step, based on the most common causes. Pair it with a liquid test kit and clear photos, and see an aquatic vet or a trusted local fish shop for a valuable or seriously ill fish.