Somethings eating my moms...but its not a pest

Hey guys!

So for the past few....months ☹...ive been noticing this deterioration in my mom plants. Its not picky as to which plants i see it on, its in both my dwc and my flood trays.... any one seen this before?

There arent any pests to be found, besides some predatory mites. But those are mostly found in the medium (rockwool hugos)

The res are 50 gal, and kept at ppms of 600, and ph of 5.8 - 6.2. 2 res' feed 36 moms each at full capacity. 2 x 5 min watering cycles per day, every 12 hrs.

Thanks!

 

Good looking out