I haven't checked ppm but always checked ph going in around 6.5
The runoff is around 5.0 .
That's what I thought and that's your problem right there..
first I recommend you spend ten bucks and get a PPM meter I use mine 10 to 1 compared to my pH meter
Second I recommend you do a heavy flush using two or three times the volume of the pot with a pH of 6.5, no nutrients because you're very likely building up salts and whether you are or not the flush will raise and reset your soil pH some
Next it's imperative you get Dolomite lime and feed one level tablespoon per gallon of pot size; example: in a 3 gallon pot add 3* level tablespoons of dolomite lime, and water it in, don't broadcast it on top
(* start with about half the amount and add up as the pH run off dictates because if you go too high with your pH it's very hard to lower it)
I was a hydro guy and when I started growing again about five years ago using
ffof soil I had the exact same problem you had, that's why I recognized it right away on your plants, highly recommend you follow these three steps I've outlined above and if you have any questions feel free to tag me in, best wishes!