How it works, honestly
This is an approximate model, not an analysis of your water. It uses the same figures as the rest of the site: free chlorine between 0.5 and 2.0 ppm and pH between 7.2 and 8.0, as required by Spain’s RD 742/2013 (ideally 7.2 to 7.6). Above 7.6 chlorine loses strength, and above 8.0 it barely works. The “Your pool this week” case uses the real 7-day forecast for Humanes de Madrid, our base: each day uses up chlorine according to its high temperature and its sun (UV index).
Every day without care uses up chlorine: we start from 0.3 ppm a day at 25 °C, and more in the heat, just like our chlorine predictor. When the chlorine that actually works falls below 0.5 ppm, algae start to grow, faster in warm water. In a real pool, sun, swimmers, rain and stabiliser also play a part, so your water may go faster or slower.
To know how your water is today, measure free chlorine and pH with a test kit or with our strip reader.