They are not doing fine on 2900 ppm. All of your plants are suffering from burn and heading towards lockout. The dry back wouldn't have helped but it's not the cause of the problem. The salts are too high and the roots are not up taking nutrient. The plants is using the stored nutrients in the leaves to keep itself alive.
You need to give them plain ph'd water for about 4 or 5 days to try and get the roots to feed again. Then just give them A + B at 500ppm.
You can grow huge plants and a big harvest and never go over 700ppm and your plants will be healthy from start to finish. It's good to learn to grow this way and learn how to read the plant before you start trying to push high ppm's.
