If you are looking to change your pink hydrangeas blue. then Hydrangea Colourant is ideal.

Hydrangeas that grow where iron or aluminium salts are present tend to change colour and produce blue flowers. Depending on The variety. pale pink hydrangeas will turn blue best with darker pink varieties turning to mauve or blue.

Best results are obtained with plants growing in acid soil. but if your soil is alkaline The proportions should be doubled.