3x3 autopot

Both double grape had leaves showing burnt tips and margins. Removed most affected leaves. New growth seems healthier after first top dress feeding. Growing in 3.9gal auto pots with FFOF, natures living soil, perlite and some pumice stone at the bottom of the pots with air domes in each pot. Autopot reservoir has a PH of 6.8 and has nothing but RO water that has been adjusted to proper PH. I have fed once with Gaia green all purpose, power bloom and worm castings by turning off the auto pots for a day the top dressing and watering in with PH’d water and recharge. Any help or comments are appreciated. This is my first time growing in 10 years. I forgot how fun it is.