Summer is in full swing, the sun is out and the water in your pool has just passed the symbolic 30 °C mark. For swimmers, that is pure joy. In the plant room, it is action stations.
Very warm water drastically changes how chemicals behave and calls for an entirely different filtration regime. Fail to adapt and the water will turn green within hours, while your energy bill takes off.
🦠 The explosive cocktail: heat, UV and bacteria
As the water temperature rises, three things happen at once:
1. Bacteria and algae multiply fast
Micro-organisms love heat. Above 28 °C, their growth is no longer linear but exponential. A small lapse that would go unnoticed at 22 °C turns into cloudy or green water in less than a day at 30 °C.
2. Chlorine is destroyed quickly by UV and heat
Free chlorine — the part that disinfects — is extremely volatile under the sun's UV rays and at high temperature. Even with correctly dosed stabiliser, chlorine consumption can double or even triple during hot spells and heatwaves.
3. The water saturates
Warm water "sweats" — it evaporates — which concentrates minerals and chemicals, especially limescale and stabiliser, in the volume that remains. Warm water also dissolves oxygen less well, which favours algae still further.
⚙️ The golden rule of filtration
You often hear the rule of thumb: filtration time = water temperature ÷ 2. So for water at 24 °C, you filter for 12 hours.
But be careful: that rule stops at 28 °C. Above 28 °C, you usually need continuous filtration, around the clock — or at the very least filtration through the whole sunny, swimming part of the day, say from 8 a.m. to 10 p.m. The water must never sit still in the middle of the day, or it will turn almost instantly.
⚡ The double penalty: the hidden cost of summer
Keeping a pool clean at 30 °C is expensive, for two reasons:
- Chemical over-consumption: you add chlorine tablets far more often, you correct a pH that drifts faster with heavier use, and you sometimes have to use preventive anti-algae products.
- The electricity bill: a standard 1 hp filtration pump (750 W) running around the clock uses 18 kWh a day. At today's electricity price (around €0.25/kWh), that is €4.50 a day, or more than €130 a month for the pump alone.
💡 Automation to the rescue
It is exactly this summer complexity that makes automated management worthwhile — whether to avoid throwing money away on badly scheduled filtration, or to avoid missing a collapse in chlorine level.
How a solution like PoolNexus saves you money in summer:
- Filtration time adapts on its own: by reading the water temperature in real time, the system works out for itself whether to filter for 10, 14 or 24 hours. If a storm cools the pool to 25 °C, the pump eases off automatically. That is how you get value out of every kWh.
- Continuous ORP monitoring: PoolNexus measures the disinfection potential (ORP). If it drops sharply because of intense heat or heavy use — a pool party — you are alerted immediately so you can add chlorine before the algae appear.
- Variable-speed pump control: for real savings, the future belongs to variable-speed pumps. A connected system can run the pump at low speed — using very little power — around the clock for faultless water quality, and speed up only during heat peaks or after adding treatment.
Conclusion
A warm pool demands faultless discipline. Once you understand the link between temperature, treatment effectiveness and the need to keep the water moving, you avoid nasty surprises. And by handing that monitoring to a connected controller, you can finally enjoy your pool at 30 °C with a clear head — and keep the energy bill in check.