You use Buffer/Alkalinity Increaser (Sodium Bicarbonate)
Recommended levels are 80-150ppm.
200g / 7oz will raise the total alkalinity by 10ppm every 10,000 litres / 2640 gallons.
Fill up a bucket of water from the pool, add the required buffer to the bucket (approx. 2 kg / 4.4 lb at a time), mix and distribute around the pool whilst the pump is running.