I've seen yellow tips but never the top multiple leaves turning a pale yellow. This is a 4 week NL in hydro on a Humboldt regimen of Oneness, Ginormous, Sea Cal and Sea Mag. The bottom 2/3 of the plant look good and the roots look normal. These top leaves don't seem to be drying out or even looking unhealthy, just yellow. I'll post a pic as soon as my camera battery charges.