When guppies crash after a water change, people often blame “bad water” or assume a disease appeared overnight. In many tanks, the simplest explanation is the correct one: chlorine or chloramine exposure. Most Australian tap supplies use disinfectants to keep water safe for humans. Those chemicals are harsh on fish gills and can damage beneficial bacteria too. Dechlorinator is cheap — but it only works if you use it correctly, every time.
The most common dechlorinator mistakes
- Forgetting: the bucket gets filled, the phone rings, and the water goes in untreated.
- Underdosing: dosing for “some water” instead of the actual volume changed.
- Guessing tank volume wrong: substrate and decor reduce volume, but not always by much — measure once so you dose accurately.
- Treating the tank instead of the new water: it can work, but it’s easier to be consistent treating the new water first.
Chlorine vs chloramine
Chlorine can gas off over time, but chloramine is more stable. Many supplies use chloramine, which means “letting water sit” is not a reliable strategy. A proper conditioner is the safe default.
How to build a foolproof routine
- measure the water you’re changing (bucket count works)
- add conditioner to the bucket before it hits the tank
- mix briefly, match temperature, then add
- keep conditioner in the same place as your bucket so it’s hard to forget
Signs of disinfectant exposure
Fish may gasp, clamp fins, hang at the surface, or become lethargic quickly. If this happens, add conditioner immediately (dose for full tank volume), increase aeration, and avoid further stress while the system stabilises.
Dechlorinator isn’t exciting, but it’s one of the highest-impact habits in guppy keeping. Most “mystery crashes” become preventable when you lock in a consistent conditioning routine.
