Top leaves yellow

No diary = no information. We can tell you what we THINK is the problem but without a diary to show us what you've actually been doing or are doing, we can't really give you a good answer as to what to do to fix the problem. This LOOKS like a calcium deficiency starting - but is that because you're giving it too much nitrogen and now have a lockout? Or is it because your pH is out of range and the plant can't get at the calcium that is available in all nutes you're giving it... don't know. And if either is the case, just throwing calmag at it is not going to solve the problem. Start a diary. They help us help you... Reconstruct as much of a diary as you can and re-ask your question... Good luck...

I am thinking light burn. Plus heat level. You have tacoing on one leaf. So I am guessing it is getting pretty warm.

I am thinking "minor nutrient"/trace element deficiency. Problems in the top/newest leaves can usually be attributed to a trace element deficiency, which are classified as immobile nutrients, hence the newest growth being affected, as there can be no translocation of these elements to where they are needed. Macro nutrients like nitrogen, phosphorous and potassium are known as mobile nutrients and this is why the deficiencies show up in the older leaves first, as these elements get moved around by the plant to where they are needed to provide health in the new leaves, hence being classified as "mobile nutrients". But without a diary and more information, it is impossible to say for sure what you may or may not be doing. Like pH, feeding, growing method etc. etc. as it could also be associated with all these things too..... too much feeding combined with the wrong pH causing "lock-out" maybe. Or the beginning of nutrient salt toxicity due to feeding too much and not watering to run off each time. So many possibilities,.... so little information to go on.