Can anyone tell me what's causing this rippling of the leaves?
Come to think of it, it looks like the beginning of an over watering issue. The soil is probably too to firmly packed down and the roots aren't getting any air causing this twisting you're seeing. I had to refresh my memory but I have had a plant do this exact same thing when the soil was just too wet for too long.
Once thing you can do is aerate the soil with a long screwdriver or something similar. Pop several holes. This helps with loosening up the soil a bit and getting some oxygen back down there to help things dry out a bit. This has saved me many times.
In any case, good luck and let us know how it goes.
I still think its a big pH swing... check your media pH if you can
6.2 seems alright... hows the new growth since you aerated the soil?