Brown patches on leaves

I don't see any blue shade on the leaf, so i'd lean Ca or Mg deficiency. if there's no interveinal chlorosis, i'd lean Ca-def. But, those are symptoms and not necessarily the cause. Do the math on your PPMs of what you feed - guaranteed analysis labels can be trusted. If you find that you provide plenty of each, it's more likely lockout and you need to investigate further to avoid the problem in future.