Leaf problem

I have an otherwise healthy looking plant with one leaf with yellow brown spots. I am using Ocean Forest Royal Gold Tupur 70/30 mix. LED quantum board lighting. Plant is 6 weeks old today. Up potted to 7 gallon 10 days ago. Watering with RO water ph 6.5. Watered with Cal Mag Xtra about 5 days ago, any thoughts would be appreciated

is it just in the down leaves? how I can see is just in one side but i can't apreciate pretty well. I'd like to descart bugs or nutrients problems, because there are some nutrients that present simtoms up before and another down before.

I wouldn't worry about it unless those spots begin to spread...not to trivialize what is possibly the beginnings of an issue, but you don't want to go treating for something until you're sure there's a problem to start with. Is it possible that you splashed water on those leaves mid-day/mid light cycle? When my plants start getting big it's not uncommon to get a handfull of lower leaves with spots like that, but I never concern myself with it unless they begin spreading.