What do I use to reduce the ph level of my lawn

Thank you for contacting Yates.

Generally speaking, regular application with lawn fertiliser such as Dynamic lifter liquid or Weed n feed will keep the soil pH acidic as the ammonia and iron content in these products. However, if the soil is very sandy and the seashells in the soil will continue to break down which maintains the alkaline reading for pH. In that case, foliar feeding is necessary to supply extra nitrogen to encourage healthy lawn grass growth. 

For young lawn, try "Munns Professional Lift Off Lawn Fertiliser". Special formulated NPK and seaweed help stimulating root growth for new lawn from turf or seeds. Please click on the following link for more information: http://munns.com.au/lawn-fertilisers/professional-lift-off-lawn-fertiliser