I'm using bio bizz light mix amended with perlite and worm castings. I'd be surprised if it was a PH issue, but I guess I'll have to test runoff the next time I water. I've been using the same PH level in my water for several months now. Between 6 and 7, about 6.5 on average. I did check runoff a few months ago and it seemed fine, so I hope you're wrong
Could it be a mix of calmag def + wind damage?