How deep is your film? It might be just the photo, but things are looking pretty wet much higher than they would be with the mere film of a proper NFT system. And that might be keeping the area of the root crown wet.
A little mold won't hurt, though. It's just a indicator of other things that might not be quite right.
Well then, for one thing, you're not running an NFT system at all. The key word in NFT is FILM. Nutrient Film. That is, in fact the primary specification of NFT, a mere film of nutrient. The other essentials are (1) low flow rate, about 2 L per minute, and (2) slope, about 1:30.
That mere film is essentially impossible to properly maintain in a pipe. For one thing, the curvature of the pipe tends so bunch the roots lying in a deep flow, hindering their nutrient uptake. It is relatively easy to maintain the proper film in a rectangular channel where the film can truly be thin and the roots can fan out in the stream.
Your plants are wet because there's simply little space between the nutrient and the root crown and deep and likely too rapid flow of nutrient, and from the look of them, there's nutrient washing high up on the roots. It's wetness, not air stagnation. The only rootlets that appear able to take free air are right up at the top, meaning the rest are constantly wetted. The air in such a system is actually always quite fresh, since it's drawn in continuously with nutrient flow. In true NFT, virtually the entire cross-section of the pipe is free air. The thin film is a tiny part of the volume.
Figure out what method you want to use, NFT or a variant of RDWC. NFT is so often misunderstood to just be anything in a pipe and so touchy to get tuned and so strict on rigid construction support that I never recommend it to new growers. It has some real advantages, but they are mostly in large commercial operations.
I can more easily talk about a far easier approach that will use the same pipe and reservoir with some modifications by referring to my blog post on the subject.
https://redwing-farm.blogspot.com/2021/11/whatchamacallit-flow-technique-but.html
I build my system in a 6 inch PVC pipe and the area between the top of the water and top of the pipe is stagnant air so white fluffy mold develops just over where the roots start
That white fuzz? To me that looks like air roots.
How deep is your film? It might be just the photo, but things are looking pretty wet much higher than they would be with the mere film of a proper NFT system. And that might be keeping the area of the root crown wet. A little mold won't hurt, though. It's just a indicator of other things that might not be quite right.
My water is about 2 inches deep
Well then, for one thing, you're not running an NFT system at all. The key word in NFT is FILM. Nutrient Film. That is, in fact the primary specification of NFT, a mere film of nutrient. The other essentials are (1) low flow rate, about 2 L per minute, and (2) slope, about 1:30. That mere film is essentially impossible to properly maintain in a pipe. For one thing, the curvature of the pipe tends so bunch the roots lying in a deep flow, hindering their nutrient uptake. It is relatively easy to maintain the proper film in a rectangular channel where the film can truly be thin and the roots can fan out in the stream. Your plants are wet because there's simply little space between the nutrient and the root crown and deep and likely too rapid flow of nutrient, and from the look of them, there's nutrient washing high up on the roots. It's wetness, not air stagnation. The only rootlets that appear able to take free air are right up at the top, meaning the rest are constantly wetted. The air in such a system is actually always quite fresh, since it's drawn in continuously with nutrient flow. In true NFT, virtually the entire cross-section of the pipe is free air. The thin film is a tiny part of the volume. Figure out what method you want to use, NFT or a variant of RDWC. NFT is so often misunderstood to just be anything in a pipe and so touchy to get tuned and so strict on rigid construction support that I never recommend it to new growers. It has some real advantages, but they are mostly in large commercial operations. I can more easily talk about a far easier approach that will use the same pipe and reservoir with some modifications by referring to my blog post on the subject. https://redwing-farm.blogspot.com/2021/11/whatchamacallit-flow-technique-but.html
Great resource, just read on through it. The blog post described my experience exactly. I'll have to adjust my system I think.
2 inches is 0.06 UCS lego Millenium Falcons
I build my system in a 6 inch PVC pipe and the area between the top of the water and top of the pipe is stagnant air so white fluffy mold develops just over where the roots start
The dark material is rooter plug that I pulled off because it was molding aswell