Looks like ph spotting due to the ph too low but it’s hard to tell as it looks like the pic is taken under a hps.
You need to flush that plant with at least 3x pot volume with the desired ph level, soil 6.5 ish, coco 5.8 ish. Then measure the last bit of run off and if needed flush again if it’s still not at your desired level. Obviously take them to the bathroom or over a sink.
I have had this problem before when not feeding with enough volume to get the necessary 10-30% run off in coco and the ph swung real low.
Hope this helps pal and happy growing👍