For a phosphate reading up to 1ppm (1000ppb) add Starver® at a rate of 500mls per 50,000 litres of water every 2 – 3 days. For a reading greater than 1ppm (1000ppb) but below 2ppm (2000ppb) add Starver® at a rate of 1 litre per 50,000 litres of water every 2 – 3 days.