Kinda looks like it's nute burn. But if you are only using 1/2 a teaspoon per gallon every other week, not sure. Maybe your soil is a strong mix.

Do you have drain holes at the bottom of your 5gal buckets?

Have you flushed them in these pots?

How do you judge your moisture level in your soil before your next watering??

CGI::::::
CanGroIt Reviewed by CanGroIt on . 33 days into flowering, strange spots. nute burn or possible deficiency? Pic's. Hey folks, I just noticed these spots today on BOTH plants. They are mostly on the top fan leaves. I had problems earlier in this grow, corrected it and for the last 5 weeks things have been going good until now. Here is some more info and pics. What is your experience level? (first timer, novice, experienced...) Novice. Been at it for a few years. Your Equipment: .1) Type and wattage of lights. 90 watt LED + 2 x 42 watt cfl .2) Distance from tops? A few inches Rating: 5