I've been doing some testing with my new DO meter, and come to the conclusion that the DWC isn't effective because it raises DO levels (it doesn't really above average levels, it prevents it from dropping if anything), but DWC is effective, because the actual air bubbles passing through the roots, and root hairs, and getting caught up in the root pores and such. So its the actual air bubbles, not DO levels.
make sense?
Never heard anyone conjecture that before.
Preventing the DO from dropping is raising the DO. To saturate above normal saturation levels however takes alot of bubbles or a lot more surface turbulence than is neded just to maintain normal saturation levels. If you do not believe this possible go just down stream of a water falls, or water rapids and check to see if the water is not higher than before the water fall or rapids. Go to a dam and check the DO level below the water spillway and compare it to the DO level for the water before it enters the spill way. Check the water DO level in a hot tub or whirl pool that has not been running for few days, then turn the pumps and air on let it run for a few hours and check the DO level. All the above example will start at normal saturation levels for the water temps but after the turbulance and air etc the water will all have a saturation above normal for the water temperature. If a buuble takes longer to reach the surface then more of its oxygen enters the water. This means if the bubble is stuck to a root more oxygen will enter thwe water from the bubble. That is true. But the oxygen will enter the root s throughthw water at thesame time rate as it would enter the water without being stuck to the root. It is a matter of time the bubble is inthe ater anfd the size of the bubble. Little bubbles have more surface area per volume so they have more surface area in contact with the water so more oxygen makes it into the water.
This will probaly insight some negative response but plants roots do not need all the oxygen we put into the reservoirs usually.
Plants roots do have a limited need for oxygen.
The problem is the water must maintain high enough DO oxygen levels where ever it is in the entire system to prevent anerobic bacteria from multiply in any area of the system. That means the water in any part of the system such as after the roots extract their oxygen needs must also supply the oxygen needs of any other aerobic bateria in the system and still have a bit of dissolved oxygen in it before it gets back to the reservoir where is has its DO boosted again by a pump or airstones etc.
If at any point the oxygen level drops to near zero or some say below 2 ppm anerobic bacteria will start growing. And where does this have the greatest chance of happening? Any place where the waters flow is slowed down and is also in contact wih the roots or any organic substances that can feed bacteria, ie dead root particles and such. This happens whether water sits stagnant around roots in aero tubes, in cracks and crannies (espeaially if they trap old dead root apartcles there. Yes parts of ther oots systen are always dieing and being replaced by new roots).
This low water DO problem also exists whereever roots are in contact with any surface and appears stuck to that suface. That root area in contact with the surface gets a limited DO in that area so it therefore so aerobic bacteria can develop there. That is the reason that root mats should be used in the bottom of NTF and small aero tubes as it keeps water moving between the roots and the bottom of the trough or tube. That is also the reason that troughs, tubes and tables should have a good drop in elevation to the drain side so that none of the waters is depleted of DO before it makes all the way through all the roots, cracks and crannies. Even ebb and flow tables gain by the root mats. This greatly lessens incidences of root rot in all systems where the roots would others wise be in contact with a surface.
This whole situation is magnified by the fact that the beneficial bacteria and the aerobic bacteria grow/multiply better at higher temperatures and use more O2 so compete more with the plant roots for the O2. In a battle between aerobic bacteria and plant roots for O2 the bacteria will win. So we really supply most of the DO we do create in the reservoirs to prevent
aerobic bacteria from developing in large numbers around roots areas.'
Some people simply run lower DO and keep both the aerobic (O2 loving) bacteria and the anerobic bacteria (O2 hating) from ever reaching large numbers.
