Leaves turning yellow, brown

I believe Fox Farm soil is time release, meaning the nutes won't necessarily be available all at once. But with watering the encapsulation slowly disolves allowing more fertilizer to become available. This then builds up, sometimes too much and thats when the burn happen. What u are describing is classic fertilizer burn- first tips of leaves and lower leaves. Are you adding cal/mag? Seems like the leaves are starting to "taco"....