My lovely blue hydrangea has gradually over 5 years changed its colour to a mauvy dirty pink with purple tinge.

I understand i can bring the blue colour back by using acidic fertilizers..... What best choice products do you recommend from a uk garden centre or maybe from B&Q Also what product would give the quickest result.

I know pure peat is acidic but i dont wish to use peat even if it was available in the stores.

Your help would be appreciated.
Regards
Ken