That's not spider mites. The blotches are WAY too large. Mite damage presents first as tiny speckles high on the plant, especially in hot grow rooms. If that were insect damage, I would lean towards thrips instead. The pic is a little blurry. Can you steady your camera better so we can get a clearer picture of the damaged leaves?

It's also not Magnesium, which presents as pale striping between the veins, in a very regular pattern that is easy to spot.

You need to be adding CalMag Plus and doing regular soil runoff pH tests if you run RO water. And you need a gallon of medium per foot of main stem. If you suspect rootbound, why are you waiting? Happy feet makes happy plants.
stinkyattic Reviewed by stinkyattic on . Light brown spots on fan leaves Hi. I have a plant that's somewhere in its 5th week, the first week of flowering. I just started noticing some light brown spots on some of the fan leaves. The plant is a really short and dense plant. I don't mean short like it looks stunted, I mean the nodes are really close together. I've looked at some of the plant problem photos that I found somewhere else, it doesn't look too much like any of them. It's in a pretty small pot so maybe being root bound can cause this? I gave it a big Rating: 5