Yellowing /brown in the center of the leaf

this looks to be a start of ph issue. a ph issue will lock out other nutrients and it looks like it is early so you can fix it and get on track, heres how. first flush your plant until your run oh ph is at a 6.0 reading, next let your pot dry out a few days, when you start the nutrients again use half of what you are using and add cal mag into the mix. you should she new growth that will be healthy, also keep your eyes open as far as the leaves that show damage they may or may not recover. if they do great if they dont great, just cut off the damaged leaves so the plant can send energy to the healthy grow. hope this helps