Brown spots

Without more infor on fertilization over the last few weeks, it's tough to be certain from this symptom. It relates to a few distinct things, but not 1 alone. What we see: Burnt leaf tips and margins... If new growth is also a bit yellow, This could be a p-toxicity. If new growth is also a bit yellow, this could be K-toxicity, The difference here is you'd see some chlorosis and curling of lower leaves, too. Could be S-toxicity, too. I'd expect darker leaves, if this were the case, but still possible because this is very early in progression. If you are soilles/hydro and feeding above 70-90ppm P or above 200ppm K, that would help narrow this down. I'm not sure where S-tox occurs, but 100ppm should be safe from personal experience. I've never see an S-tox first-hand. A k-deficiency would start around the tips, but would come with chlorosis and interveinal spots... again, this is such an early stage it might present itself as it progresses. If none of what i mention jives with what you've done/know that is not listed here, and it is slowly progressing, I'd suggest being patient and seeing how it progresses to be more certain about diagnosis.