Help dwc system problems

Text ppm? Do you mean check? Get a ppm meter. Dip it in the water and it will flash the ppm at you. What strength light is that? Looks very close.

something like this.

I have ran into this problem years ago and I changed everything around backwards and forwards couldn’t figure out the problem then one day I was in that room and I happened to notice the line on the wall from the reflection from my hood It goes all the way around the room and you will know when you would look anyway it just didn’t look right
put a new lightbulb in lol it was that simple
Change both bulbs I am assuming you use 2 bulbs one on each end of the spectrum Veg/flower HPS/MH every grow ??

Did you get it as a clone from someone? Havent got mites or anything do you? Have a look at inderside of leaves. May need a jewellers loop or something similar. Just a thought??