Goldfish Dead in 10 Minutes After Water Change: Chlorine Poisoning

2 goldfish (black moor, comet) in tank. 50% water change with tap water (no standing), dechlorinator used. Fish gasped, swam erratically, smelled like chlorine. Moved to aged water—died in 5 mins.

Diagnosis: Acute Chlorine/Chloramine Poisoning

• Smell + rapid death = high chlorine.
• Dechlorinator may be insufficient if municipality uses chloramine (chlorine + ammonia)—need ammonia-neutralizing conditioner.
• 50% change is too large—causes osmotic shock.
• Tap water gas supersaturation can cause gas bubble disease.

Correct Water Change Protocol

1. Weekly 20–30% changes.
2. Use conditioner for chloramine (e.g., Seachem Prime).
3. Don't remove fish—siphon directly.
4. Age new water 24 hrs with aeration if possible.
5. Test tap water for chlorine.

Report It

Call water supplier—utilities sometimes shock-chlorinate lines, killing aquarium fish. Complain officially.

This was preventable. Small, conditioned, frequent changes save lives.