Is this a deficiency?

I think it’s a potassium def. the yellowing edges are a sign of it. It’s present on new and old growth, and being an immobile nutrient it makes sense. If it was a mobile nutrient I feel your new growth wouldn’t look light/yellowed at all and only the bottom older growth would be showing signs as the new growth would draw from it. Jmo Happy growing

oh, theres a multi product nute calculator i host on a google drive link too.. on profile.

Based on diary, i'd guess overabundance. Dial back. Unless you check your labels and find a total lack of something. check my profile out, i made some common links with great information. "maximizing cannibis yields" around minute 44? 9/10 times it's because you have fed too much. check labels, calculate your ppms.. knwo what you feed so you can deduce what hte issue is later. have an EC meter? this would eliminate my suggestion easily. It should be done first before adding anything to your soil. or, just flip the coin and see what happens :P

Yes that is a magnesium deficiency, A light green or yellow coloring will begin to show on the veins and edges of the lower & older leaves – this is one of the classic signs of cannabis magnesium deficiency. You may also see red stems. Magnesium is a mobile nutrient, which means that the plant can move it from old leaves to new leaves.