Just got through reading heaths tree thread at eye see and I gotta say he fuckin killed it with his RDWC. 4 lb plants with 3 600's...
The key is to have a chiller that can keep your water at around 66 degrees or less to take advantage of the higher DO levels associated with colder temps, but not so cold that it really inhibits nute uptake. Lots of water movement. upsize everything. Heath recommended a 1000L/hour pump size for each site. You need to have lots of flow, but not be blasting the roots so hard that you damage them.
From my notes:
Here's some info from Heath about D.O :
"In this you can see that at 19 deg C its about 9mg / L of DO, so not quite 1 mg for every C the temps are raised but a useful rule of thumb. this is sufficient for healthy plant growth, the optimum for nutrient temps is between 18 and 24c
As growers we are caught in a "catch 22" situation because DO is increased at low nutrient temps but the plant growth is regulated by performing countless numbers of biochemical reactions which will double for every increase of 10 degrees C degrees or on the other hand be cut in half for every reduction of 10 degrees C, so there is the dilemma...... which leads me on to some possible answers
The recirculating systems I use all rely on one simple fact and that is whenever air is in contact with the water, whether through natural or artificial means, a transfer of oxygen from the air to the water takes place at the surface which provides a good gas exchange allowing oxygen to enter the water and carbon dioxide to escape until the water becomes saturated. The speed at which oxygen from the air enters and mixes through a system depends on the amount of agitation at the water surface, the depth of the system and the rate at which it mixes itself.
When normal airstones are used most of the DO is obtained when the bubble forms and then by water movement at the surface, so most of the DO is created by water movement at the surface rather than bubbles as most people think. Another thing growers should consider is the practice of placing a large airstone underneath the roots and allowing it to bubble away furiously can cause mechanical damage to the roots and the turbulence can cause stress. Much better to have the bubbles generated in a remote rez and recirculate them through the system.
Ceramic Micro air Diffusers (CMD) are brilliant for aerating your system, if you have never seen one running you are in for a treat, when you first run one its a surprise to see what looks like milk streaming out of the diffuser! or a bit like underwater fog, with one of these you can oversaturate depending on the size of the diffuser or system but not to the point that the system is toxic. If you decide to use one of these, depending on how good the CMD is you can run them intermittently as the DO will stay in the system for about 20 mins .
I wouldn't recommend the use of CMD with oxygen as you would run the real risk of it becoming toxic but not at the levels you suggest it would have to be more than double 14mg DO / L."
"The water comes into contact with the air in the rez and also around the inner pot. If you notice all these systems have a external rez which the water flows from and back to. Whenever air is in contact with the water, whether through natural or artificial means, a transfer of oxygen from the air to the water takes place until the water becomes saturated. so it doesn't matter that the inner pot sits in the water as the water is already fully saturated with air from the rez. I hope that makes sense.
Ok just to make things as clear as mud here is a summery of whats been discussed so far.
Dissolved oxygen (DO) is one of the single most important factors in hydroponics. If DO concentrations are low plants cannot take up nutrients, they will grow slowly or not at all, and they will be susceptible to disease. where concentrations are very low, plants may die from lack of oxygen.
Wherever water is in contact with the atmosphere, oxygen from the air will enter the water until the pressure of oxygen in water and air are equal. This is known as equilibrium or saturation. The concentration of DO at saturation increases with increasing pressure and decreases with increasing water temperature.
When water contains less oxygen than the saturation concentration, oxygen from the atmosphere diffuses into the water, Oxygen will be added to a recirculating system at almost any point where the water surface is in contact with the atmosphere.
The addition of a air stone can be useful but not in the way that most growers think. If the recirculating water is at full saturation then the addition of air stones wont make any difference whatsoever, if the water is low in DO for whatever reason, then the addition of an air stone would increase DO simply by the action of moving the water and allowing more contact area at the water surface as I mentioned earlier "Wherever water is in contact with the atmosphere, oxygen from the air will enter the water until the pressure of oxygen in water and air are equal". This can also be achieved by simply placing a small submerged pump in your rez.
Good diffusers and Protein skimmers will add Do because of the small bubble size they produce, typically less than 1 millimetre (mm) in average diameter, compared to 3 to 5 mm or more for aquarium type air stones. For example, decreasing the bubble size from 2.4 mm to 0.4 mm would increase the contact area between the air and water by a factor of five. An additional benefit of small bubbles is they take much longer to rise. A good diffuser will supersaturate your water which wont directly benefit the plant as it cant use the extra DO but it might indirectly help by increasing the numbers of beneficial bacteria and reducing harmful ones.
I hope that helps clears things up because we are in danger of sending everyone who looks in to sleep
Heath"
Do a lot of reading here and wherever you can, and if you have any questions on an MPB I can help since I am probably one of the only ones left that actually runs one. LOL.
-Cap
