Hey Ash, basically i've been looking at your photos and what i can see is that you don't actually have pests. That's good news but prevention is key : make sure all intakes have a maximum 90 micron mesh screen protecting them from intruders like mites and other pests; if you're nervous buy some live ladybugs (its actually the only thing that truly works strange but true !) and release them in the grow room. Otherwise what I think might have happened is that the leaf got damaged when you were moving the plant when it was young or something. those brown spots are probably nothing, but just to make sure I would simply add some cal mag because it looks a little like the start of magnesium deficiency. Good luck with the grow ! ๐