Why algae grows in your pool in the summer

Algae need light to grow, strong sunshine is algae’s best friend. Just when we are getting our pools ready for the warm summer days the daylight hours start to increase, just what the algae need. It is worth taking a look at just how the light in the UK varies throughout the year.

Below is a  graph on which the blue line is daylight hours.  Note how all through June and well in to July we get 16 hours of daylight per day compared with 8 hours in winter. Twice as much daylight in summer as in winter.

The next graph shows the altitude of the sun. Note how in summer when the days are 16 hours long the sun is up to 60 degrees above the horizon but in winter is barely gets above 20 degrees. The lower the altitude the more atmosphere it has to penetrate, the lower the strength of the light. The opposite in summer, lots of light and lots of strength.

That is why algae grows so much more in the summer than it does in the winter. Light = food for algae, give something twice the amount of food and it will grow twice as much