browning leaves

Alright, here's my set-up (more information in the thread linked in sig.):     Lighting: 128 Watts (4x 32W T8 6500k bulbs) - 8 hours a day (on a timer, so it NEVER changes).   Tank: 6 foot, 110 USGallon tank, roughly 22 inches from lights to substrate.   Substrate: Sand     Plants in tank:  ...