Good job on your first grow, man. You're bringing home some psychedelic bacon. +1 on the Radio Shack microscope. I use that. Also when red hairs are coming faster than white hairs, that's an indicator. Instead of flushing, a lot of times I just water with plain water at the end. I would say let it go two more weeks watering with just plain water and that would be equivalent to a flush without the hassle. When you get some yellow leaves around harvest, that shows you that there's a deficiency and hence a 'flush' of nutrients happening.