I’m growing the same way. I think your EC is a little high. I would recommend bringing it down to 1.0. I think 4x a day is fine. I’ve done up to 6x a day in 3gal fabric pots.
Yucca is great as a surfactant. It’s just a pain to mix in powder form. I mix the powder into a small amount of warm water to dissolve the powder, then add to the res.
For salt buildup, which I feel does happen to some degree no matter how many times you fertigate. I use Recharge once a week by hand. Just RO water, about 150ppm of
calmag, and the microbes. Flush all the pots well and then I resume normal auto feeding. This once a week treat does two things for me. Keeps the EC of the coco low, and introduces beneficial microbes to the root zone. The plants love it.