skyboundanswered grow question 6 years ago I suspect the mottling is a combo deficiency between Ca and K, though I'd go so far as to say that both look minor so maybe not try to fix either. If you're using nutrient salts you can isolate a specific element to tweak, but most nute brands have multiple things mixed in the bottles so if you tweak any thing, you end up tweaking several things which will cause other problems.
If interested, I made a tutorial for using Hydro Buddy to reverse engineer your nutrients, then you would be able to play around with tweaking the nutes in theory before actually changing anything in practice.
https://www.420magazine.com/community/threads/making-your-own-nutrient-concentrates.455187/