So, for about the first year I used to bubble my tap water 5gallons at a time, with air stones for 1-2 days before jugging to mix with nutrients. Now, i just rinse & refill jugs straight from the kitchen tap. Literally 0 difference in plant response, so I stopped wasting time aerating the water. Not to mention, I water our outdoor garden & flowers with the hose, and it doesn't seem to affect the soil quality in our raised boxes. We still get mushrooms & mycelium no problem.
Don't trip out on every single spot that you see on a plant, only if it's consistently spread throughout the plant. My opinion? --that spot could be from crimping the leaf every-so-slightly when doing nearby maintenance, whether LST or just spreading the leaves out to kind of look around, maybe you flipped the leaf to look at the underside?