What's wrong?!?

calmag when it has no effect is because the roots are unable to absorb magnesium due to mineral salt blocking, try to use a substrate cleaner, then make a flush and apply the calmag. Good luck mate

Is the spotting happening on the top leaves? if yes, then it is a calcium defiicency, which by the pictures it appears to be the case. The problem with calcium deficiency is that the symptoms appear several weeks after the deficiency is present. At this point there is very little you can do. your water should always have a base of 0.5 EC (250 PPM), if not then you need to add cal mag to get to that point.

@Gewroo Hi mate if it isn't calcium related then it could very well be a case of rust fungus which has a similiar appearence to your problem I found this link that may be able to provide the information you need to answer your question https://support.ilovegrowingmarijuana.com/t/rust-looking-brown-spots-on-leaves/17343?page=3 Good luck

Hey man! Plant will survive it looks strong and healthy so it will produce in the end. Check out my latest diary “want some sugar” I had one plant that did some thing very similar things with the spotting and let me tell you it only gets worse lol... I could not get a solid answer from anyone on what could be causing it. My only theory I came up with was Root problems, something was rotten or infecting my plants from the roots so it might not of been buffering PH correctly or just not up taking nutrients correctly, not enough airflow into the Medium, cold roots, bugs? not to sure. This plant was furthest away from my fans in a tent With out vents just two Exhale co2 bags, so it’s root system got the least amount of fresh air. My solution I’d try increasing airflow around your roots and do very solid watering with just Carb loaded nutrients and something just organic keep it light...hope this helps! Happy growing

Inthinkmyounmeed more calmag. i usually go with 1ml/1L throughout the grow if using any led lighting. looks like cal def