Australian summers can push aquarium temperatures higher than you expect, especially in smaller tanks or rooms with afternoon sun. Heat stress is not just about “warm water” — it’s about oxygen availability and how quickly conditions swing. Warm water holds less oxygen, and stressed fish breathe faster, which can spiral quickly if you don’t respond early.
What temperatures are risky?
Many guppy tanks run happily at 24–26°C. Short spikes to 27–28°C are usually manageable if oxygen is high. Problems tend to increase when tanks sit near 29°C for extended periods, especially if the tank is crowded or filtration is weak.
The real priority: oxygen
- Increase surface agitation: aim the outlet toward the surface.
- Add aeration: an airstone or sponge filter is a quick win.
- Reduce waste load: feed lighter during heat waves so oxygen isn’t consumed by decomposition.
Safe cooling tactics
- Fan cooling: a small fan blowing across the surface increases evaporation and can drop temps by a few degrees.
- Light control: reduce photoperiod and avoid hot fixtures over the tank.
- Block sunlight: direct sun can spike temperatures fast.
- Small temperature-correct water changes: don’t pour cold water in — match temperature to avoid shock.
What not to do
- Don’t crash-cool: sudden drops stress fish as much as heat does.
- Don’t overfeed: heat + heavy feeding is a common trigger for problems.
- Don’t ignore early signs: surface gasping and clamped fins mean act now.
After the heat wave
Return to normal feeding gradually and keep water changes consistent. If you had prolonged high temps, watch for fin damage or appetite changes and keep oxygen high for a few days. Stable recovery prevents secondary issues.
Heat waves are survivable with guppies when you prioritise oxygen, gentle cooling, and stability. The earlier you respond, the smoother the week goes.
