Drooping blueberry leaves
I have some 3 year old blueberries in pots, all with ericaceous compost which I topped up earlier this year. One of them has leaves which have started to droop. I checked the compost, and it's moist but not too damp. I only ever water them with rainwater. Any ideas on what's causing the leaves to wilt please? I took out the top 6 inches of compost earlier and topped it up with more ericaceous compost just in case it is lacking nutrients. The other 2 plants are fine and all have been treated and watered the same way.
Any suggestions gratefully received.