Hello chopficaro,
First, I agree there wouldn't be much point to having a air
pump in the reservoir in a NFT system that's running 24/7 and has the water temps in the optimum range. The constant water flow keep the water moving, and the churning water in the NFT channels, as well as the falling water in the reservoir aerates the water. Not to mention that in a NFT system most of the oxygen uptake by the plant is done by the roots that are above the water line in the NFT channels. So adding a air pump would have little effect.
Second, light brown roots does not necessarily mean disease. Older roots will often naturally become tinted brown. Especially when hanging in mid air. Healthy roots will feel firm, diseased roots will feel mushy and/or slimy. Here is a
picture of perfectly healthy roots. You'll notice the roots are NOT pearly white, but rather brown instead. You'll also notice the older roots near the top are darker brown, while the newer roots at the bottom are lighter brown to white at the tips.
Third, your right that it doesn't mater what you put in the water, the roots above the water line won't get any benefit because their above the water. The roots would either have to be submerged, or in growing media and the water top feed to cover the entire root system.
Fourth, I'm not sure if you understood what I was saying in the other thread about the foam. In your case the foam doesn't necessarily mean pathogens because you are adding beneficial microbes. Both beneficial microbes and pathogens will give off proteins that will result in the foam. Also both beneficial microbes and pathogens can cause a bad moldy/musty smell, as well as cloudy water. The one sure difference is that beneficial microbes WON'T cause mushy and slimy roots. Beneficial microbes won't harm the plant, but pathogens will. Mushy and slimy roots mean disease, so only pathogens will cause mushy and slimy roots.
Fifth, the pH changes may, or may not be related to the microbes in the water regardless if they are beneficial or pathogens. Both can alter the pH. The continued addition of beneficial microbes will increase the foaming. Also if the beneficial microbes are affecting pH, continually adding more beneficial microbes will only cause it to get worse. But before I can determine the pH changing is related to the microbes (either beneficial or pathogenic), I would have to rule out other possibilities. So I have a few questions:
1. Do you have any pictures of the plants and system?
2. Other than the color of the roots do your plants look healthy?
3. Are the roots firm, or mushy/slimy?
4. is the reservoir water clowdy or translucent?
5. Does the reservoir water have a musty or moldy smell to it?
6. How are you cheeking your pH?
7. What are you using to adjust your pH?
8. What are you using for your water source?
9. How often do you change your
nutrient solution?
10. How big are your plants?
11. How many plants are in the system?
12. If you don't adjust the pH will it continue to rise, or is 6.7 as high as it gets?
13. Are you adding anything other than the maxigro and Hydroguard to the reservoir?
14. You said you added three 8 oz doses of the Hydroguard to this reservoir so far. What time frame are you talking. When did you change the reservoir last, and how often are you adding the Hydroguard?