what kind of toxicity is this?

14 days into flower medium is coco feeding 15ml a+b each connosuier advance nutrients 5ml big bud 5ml bud candy 5ml b52 per gallon my solution ppm reads 1000 ph 5.8-6.0 its only showing this problem at the very bottom the middle and top look great im thinking I should lower feed to 800 ppm

Salt build up and/or moisture stress. Flush with ph'd water then feed and water more often. At this stage she's at her hungriest.

I water ever 2 days it in 5 gal smart pot last runoff ppm was 1100 watered with a 1000 ppm been doing feed water feed running few gallons of florakleen through It every week or two