“New tank syndrome” is the period when a tank is still building the bacterial colony that processes waste. During this time, ammonia and nitrite can spike. Guppies are hardy compared to many fish, but they still react to instability with clamped fins, dull colour, or erratic behaviour. The biggest mistake during new tank syndrome is doing random big changes that reset progress. The best approach is a calm routine: test, adjust, and keep the system consistent.
What new tank syndrome looks like
- cloudy water after feeding or after adding fish
- ammonia or nitrite readings above 0
- fish acting stressed (clamped fins, hiding, faster breathing)
Why it happens
Bacteria don’t instantly appear in large enough numbers. They grow over time. If fish are added too fast, waste rises faster than bacteria can process.
The calm routine that works
- Test daily during the unstable phase: especially ammonia and nitrite.
- Do partial water changes as needed: reduce toxins without fully resetting the tank.
- Feed lightly: reduce waste while bacteria catch up.
- Don’t overclean filters: you need bacteria to establish.
How to avoid it next time
Seed your filter media from an established tank or run a sponge filter in a mature system before starting a new one. Adding fish gradually also prevents overload.
New tank syndrome is not a mystery and it’s not a personal failure. It’s a predictable biology phase. If you stay calm and consistent, the tank stabilises and guppies thrive.
