Brown spots calmag didnt help is it septoria?

It could be a bug feeding on the leaf.

Do you have a grow log to share? Without more information we can only guess…

Check your pH and EC first, make sure those are correct. You look like you have a potassium issue being in flower but you have to figure out the medium stats to know weather it’s deficient or what’s more likely is your pH is off causing lockout.