Phosphates are a food source for algae and will assist in its reproduction and enter the pool more than likely via rainfall, water tanks, animal droppings and fertilisers.
We recommend every 4-6 weeks you have the pool water tested for phosphates or simply treat the pool with a phosphate remover as a preventative measure, making sure to follow the product instructions and to backwash once the phosphates have been collected in the filter.
If your phosphate levels are high (above 0.2ppm) and you have treated the pool to remove them, please remember to check and re-balance the water again, especially copper levels. It is likely your copper level will be lower than ideal because it has been busy fighting the potential algae trying to grow in the pool due to the phosphates.
For adjusting copper levels, please refer HERE.