Tips of Cape Sundew are turning brown

Hi ya'll :)

My 3 Cape Sundew alba had all of their tips to turn brown. They were in a deep plastic tray with a big red Cape Sundew and several D. roundifolia (small). Nothing has happened to them. I have them sitting on a shelf at the kitchen window (west) with a 150w screw-in flouresent light about 10-12 above the plants. Water is rainwater kept about 2 1/2 in. deep in the tray. I've had these plants since last spring-summer. Whats happened?? Do I need to trim off the brown or what? Thanks for any help :)

Eric

Any ideas??