You can trim roots, just like you trim the upper part of a plant.
But do not ripped them, crush them or mutilate them; with damage comes rot.
Just cut them with a sharp knife or scissors, and don't try to cut more then a 1/3 of the root mass off. Won't hurt the plant at all, some strains it won't even slow them down some strains will need a couple of days to recover and start growing again.

When your roots grow, you'll see two types, long large roots that tend to grow straight down, these are tap roots and look for water. The smaller hairier roots are the air roots, that fan out closer to the surface looking for oxygen and probably co2 also. (some debate about the roots using co2, some science to support it).

Dutch Masters makes a product called Zone, acts as a bio-fungicide and general healthy root promoter. Works well in recirc systems.
oldmac Reviewed by oldmac on . HID & LED Iā??m in the planning stages of a DWC. It looks like itā??s going to be 6 buckets. The grow room is 5 feet wide by 2 Ā½ feet deep. Iā??m contemplating a 250W HID in the center with 1 GrowPanel 45 at each end. Hereā??s a link for the LEDā??s led grow lights -Sunshine Systems : The GlowPanel 45 LED Grow Light I need some heat as I live at altitude and the winters get quite cold and Iā??m not really interested in supplying supplemental heat just for itā??s sake alone. And the summers get Rating: 5