If you want your grass to grow well, one of the things you would do is feed it with a fertiliser which has a specific blend of Nitrates and Phosphates suitable for your type of grass. In the same way, Algae feeds on Phosphates and Nitrates too. If Algae lands in your Pool and there is a good balance of Phosphates and Nitrates, then it will grow very quickly overwhelming your Sanitiser (Chlorine/Bromine) and turning the Pool a shade of green!
You can never completely remove Phosphates or Nitrates from your Pool. These are naturally occurring and are just about everywhere; in your household water, rainwater, lawn care products and organic matter (leaves and twigs) to name a few. The aim is to keep the Phosphate levels near zero which will starve any Algae that lands in your Pool which in turn prevents it from growing.
Take a water sample from your Pool and bring along to us (or your local Pool Company) to carry out a full analysis. As well as testing other chemical levels, it also gives a Phosphate level reading. If the level is high, you will need to add a Phosphate remover to the Pool. Remember, this will only reduce the level of Phosphates and won’t kill existing Algae.