John, go to a local nursery and see if you can get lime and phosphate (or triple super phosphate). Both of these will increase your soil pH, limit aluminum absorbtion and give you blooms that are a shade of pink.

An acidic pH of around 6 or 6.2 will start giving you pink blooms. A pH reading of 7 is neutral but higher than 7.0 is alkaline.

Try not to get very alkaline soil though. If you do, the hydrangea will develop iron chlorosis on the leaves (the leaves will turn light green or yellow while the leaf's veins remain dark green). If that happens, you will have to apply liquid iron chelated products to counter act the lime. Local nurseries sell these.

Always apply per label directions; do not go overboard with these ammendments as the roots may not like it if you add too much too fast. You can change to hardwood mulch if you wish.

I suggest frequent soil tests so you know how acidic or alkaline the soil has become.

Good luck,
Luis