I built an NFT system out of 2" PVC and am having trouble getting my plants to grow. My roots are turning brown. Does anyone have any answers? Thanks.

Make sure your nutrient reservoir is heavily airated so your mixtures is 02 saturated. Your description sounds like Pythium. If all your roots are brown, Its a good idea to remove the crop, dump the tank and start over. Keep your nutrient water under 85 degrees, make sure it's airated and use a nutrient additive to populate your roots so Pythium doesn't have a place to colonize. Companion is a great product for this.

I feel that 2 inch PVC is to small. Once your plants begin to develop root mass the pipe (especially in your case) gets "choked" with roots. This slows the flow of nutrient solution, the plants at the beginning of the pipe will consume most of the available dissolved oxygen in the nutrient solution. Once dissolved oxygen levels drop in the nutrient solution, then all kinds of problems begin. Firstly root death, this then gives root rot pathogens a gateway to infecting your plants and whole system. Secondly, dead roots also give the pathogens protection from sanitizers and also a food source, thus allowing their populations to explode. Thirdly, with a mass of dead or dying roots invites fungus gnats, the larvae feed off dead and living roots. They will also burrow into the stem of the plant and kill it from within. I have seen this a few times, causing entire greenhouse crops to fail.

I feel that the first solution to your problem is to give your plant roots more room. 2 inches (height) x 4 inches (wide) is far better, or use 4 inch PVC. The second solution is to maintain solution temperature. Absolute highest is 85 deg F, ideally below 80 deg F. Also keep as much light from penetrating inside the gully, this will reduce the growth of algae which is also a food source for fungus gnats.

Also make sure your slope is 1 inch every 4 feet and that the flow of nutrient solution is 1-2 liters (quarts) per minute into the gullies.

Hope this helps.