Six Clones. First Grow!

Over the last couple of weeks I have had quite a few leaves changing color and dropping. My pH seems to be in a normal range, and I don't think I'm having a nute deficiency of any type, as my well water is mineral rich. I suspect nutrient lock-out. Though I've done some flushing in the past, it has seldom involved more than 1-2 gal of water, which I think is probably a grossly insufficient volume. I am beginning week 8 of flower today, and so I should have some trichome activity--for these strains--very soon. Currently none of the trichomes are opaque.