Ah yes, hydrangeas change as they age and it is often due to the soil changing as it becomes less acid with added fertilizers and perhaps lime added to a nearby lawn.  Lime and calcium make the soil less acid and the blooms pink. You can change your hydrangeas back to deep blue by adding aluminum sulfate to the roots six to nine months before the plants flower. For larger blooms prune so that you have fewer branches but larger flowers on each branch. Lack of water and too much heat can also cause smaller flowers. A 3 inch mulch of wood chips on top of the soil around the hydrangeas will not only keep the roots cool but also help to lower the ph of the  soil and keep the blooms blue. Gardening is an adventure so have fun watching how your plants change. Keep growing, Marianne Binetti