Currently I'm doing a side by side comparison to see if airstones and air-pumps are needed. My theory is that the recirculation of ebb and flow aerates enough as it is. I'm at day 40 and both trays look almost identical.
As I wrote before. It is not really the DO level in the resevoir or even the DO of the combined water returning to the reservoir is aerated enough to resaturate the water with DO. It is simply a case of is your system operating in a fashion where any water in any part of the system in contact with the roots ever reaching zero ppm of DO or very close to zero DO ppm.
High DO in a resrvoir is a concept blown way out of proportion. As long as all the water every where in your systems has some DO at all times there really is not anything to worry about. If your system contains design flaws where there are spots where the DO drops to below zero. Then in all likely hood, duh, if they reach DO zero ppm when starting out at over 8 ppm (fully saturated) a lower DO is staill going to simply produce the same bad results. In rteality the fact that at a few degees warmer the DO is at a lower ppm at saturation is not really an issue. What is an issue is if you do have bacteria growing in your system do to poor design the bacteria n multiply grow faster, consume more roots (root rot) and use more DO while doing so. So the scare about low er temps and higher temps simply apply to poorly designed and set up systems. Unfortunitly the majority of sy ystema are poorly designed and set up amongst mj growers. So "experts" rather than being honest say stupid things about higher DO at lower temps means you should maintain resrvoirs at lower temps. Kinda like lets ignore all the problems in al the bad systems in use by blaming it on a simple 10% decline in DO.. That is simply ludicrous. Duh, lets all grow mj less efficiently over alonger period of time just so we do not have to acknowledge we are growing mj in systems with a lot of problems that we are not fixing. As well we buy a lot or retailed systems that are poorly designed so we must grow at low temps with low resrvoir temps.
I know of many, many systems without airstones, however, any DWC system with every reservoir containing roots can easyily have spots where there is a zero DO without very good aeration or air injected opumped or released into the reservoirs.
Some of the best DWC systems have one resrvoir that contains no plants. That resrvoir is heavily aerated and a pump pushes the water through all the other sr reservoirs keeping them aerated. The inlet and out lets in the resrvoirs are diagonal opposed to create turbulence in each reservoir.
The best DWC I have seen used the same principle but also installed a venturi at the pump inlet. The pump chops the drawn in air into many, many very small bublles and these are circulated by the pump throught out the system. I have seen these set up with a dozen 25 to 30 gallon reservoirs and the water returns to the pump with only a 1 ppm drop in DO. as tested with a DO meter. The pumps are pressure biased pumps so the water is moving at a higher velocity (speed) than the typical flow bias pumps. Less volume greater speed. This means using pumps like Iwaki RZT pumps or Sequence reeflo Pressure biased pumps. The Reeflo pressure biased pumps are lower pressure pumps than the Iwaki. They run at flows and pressures in between the Iwalki RZT pumps and a common fountain/aquarium high flow pump (about 10 to 15 psi).
http://www.reeflopumps.com/pressurebiaseduno.html
There are many way to solve zero DO in areas of a growing systems. That is what people need to be looking at. many fixs are relativly simple. Things such as putting down a oiece of silkscreen cloth in the bottom of all small aero tubes and NTF channels/gutters. Growing only small plants in small tube aeros and NTF. Water unless under forve (high velocity IE high pressure pumps do not quickly move through thick root masses laying in a tube or gutter bottom. The silk screen allows flow both above and below the root mass. The higher velocity allow faster water movement f through the mass. this means that the water might possibly meake it all the way through all the roots in the tube or through without reaching zero DO. sometimes even those measures are not enough if you grow in afashion where the root masses are too large and your tubes or throughs need to be shortened. These are the typesof things that need to be lloked at, com nsidered and changed, not simply addressing DO levels in a resrvoir. In a DWC you need to worry about getting your roots moving enough so that Do laden water can circulate through out the root masses not just over the outter layer of the root masses.
Even Heath's vertical grow, sad as it is, is based upon the concept of keeping a fast flow of water moving through the systems so that the water does not reach a Zero DO anywhere. A DO meter is not needed for you to simply think through every part of your system and think "Where is the water DO going to be lowest." Now don't even think about trying to raise the reservoir DO in hopes of raising the DO in that spot that clearly will not work. Just accept your system or methodology is flawed and figure out how to increase the rate of flow through the areas that lowered the DO before the water made it to the Zero DO at that bad spot. Change those previous areas (smaller plants, silk screen, higher velocity, wider troughs, bigger tubes etc, so that the DO will now be higher at the worse spot.
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