Posted: 26/07/2016 at 10:22
Rhododendrons aren't quite as dependent on having acidic soil as azaleas and some other plants are, so if your soil is only marginally alkaline your plant may well be ok.
It sounds to me as if the hybrid has been grafted onto another rhodo, possibly R. ponticum, and the flush of strong growth and pink (pinkish mauve?) flowers are coming from the rootstock. If that's the case the R. ponticum will overtake the white flowered variety and grow into a massive shrub, totally unsuitable for a garden. http://www.forestry.gov.uk/fr/rhododendroncontrol
Have a look and see if the new growth is coming from below the graft.