looks like the start of p phosphorous deficiency, the dark bluish tints and rings that form on yellowing older leafs, the downward cupping of you're leafs, burnt leaf tips, also look for a reddish purple on you're stalks and the veins on the underside of you're leafs or on newer leafs, but that can be a strain trait or it normal shows in later stages, necrotic spots on older leafs,
what youre ppm/ ec feeding plan, medium, how often you feeding, all the basic info will help