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Rdwc - Dissolved Oxygen, Temperature And Bad Bacteria

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In another thread I posted about trying the oxydoser to increase DO in my RDWC system.

 

In doing some research to gear-up to test the oxydoser I developed some questions I'd like some feedback on.

 

Maximum DO levels based on water temperature (not adjusted for salinity, which makes only a negligible difference):

 

59 degrees F - 9.85ppm

 

68 degrees F - 9.07ppm

 

82 degrees F - 7.81ppm

 

That's not a big range of DO over a wide range of temperature.

 

I'm going to start by testing the DO in my current system. If I'm getting significantly close to DO saturation already, the only benefits of the oxydoser would be:

 

No clogged airstones

No constant pumps running

Reduction in electrical consumption

 

The downsides would be:

 

You have to buy it and a water pump (although the two needed pumps don't cost much more each than a quality air pump - the oxydoser might be cheaper for a new grow than air pumps, tubing, and air stones)

 

Louder pump

 

I also looked at different air pumps. I usually have 2-4 pumps running 24/7. They cost about $100 each. They use around 300 watts and move around 5,000 gal/minute. For $170 each I can get a high-efficiency pump that moves about the same volume of air and only uses 50 watts.

 

Cost per month to run 3 pumps.

 

Current: 3 pumps x 300 watts x 24 hours x 30 days / 1,000 x $0.12 per kW/h = $81 per month

High efficiency: 3 pumps x 50 watts x 24 hours x 30 days / 1,000 x $0.12 per kW/h = $13 per month

 

So, if I switched to high efficiency pumps they would pay for themselves in 7.5 months. Used in a similar new grow, the better pumps would pay for the price difference in 3 months.

 

I'm now trying to figure out the most cost-efficient way to reach maximum DO.

 

One concern I have about testing the oxydoser is I don't know if the DO readings would be skewed by the suspended (not dissolved) air bubbles. I can't think of a way to control for that. With airstones it's easy. Just remove the airstone and test DO when the bubbles are gone.

 

All this leads me to questions:

 

1. How much of a role does water temperature have on root rot? Does the 14% drop in DO from 68F to 82F mean the difference between healthy and nearly dead plants due to oxygen deprivation?

 

2. - or does the elevated temperature and lower DO simply provide the necessary environment for the bad bacteria to take over?

 

3. If "yes" to no. 2, can you maintain plant life with nute temps at 82 degrees by using enzyme and beneficial bacteria additives.

 

All in all, I'm trying to figure out the most efficient (time and cost) way to balance chilling water/aerating water/using additives.

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Aerocloners have taught a lot of us where the temperature line is between having pathogens and not having them. It's right at 80 f. Above that and the pathogens multiply uncontrollably. Roots grow better when the reservoir is warm. So the sweet spot is always as close as you can get to 80 degrees f but not over that. 

 

I've run a 12 site automated aeroponic set up for 8 years now. I find the best way to cool the water is to circulate the water underground and then back to the reservoir with an aquarium heater to keep the temp rock solid. Geothermal set up. 

 

I've always thought that putting an air stone in a DWC created oxygen in the water more by the bubbles moving the water than the actual bubbles themselves because of the high surface tension of the bubbles. I think a way to improve oxygen content would be to use some sort of detergent to reduce the surface tension of the water bubbles. 

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Aerocloners have taught a lot of us where the temperature line is between having pathogens and not having them. It's right at 80 f. Above that and the pathogens multiply uncontrollably. Roots grow better when the reservoir is warm. So the sweet spot is always as close as you can get to 80 degrees f but not over that. 

 

I've run a 12 site automated aeroponic set up for 8 years now. I find the best way to cool the water is to circulate the water underground and then back to the reservoir with an aquarium heater to keep the temp rock solid. Geothermal set up. 

 

I've always thought that putting an air stone in a DWC created oxygen in the water more by the bubbles moving the water than the actual bubbles themselves because of the high surface tension of the bubbles. I think a way to improve oxygen content would be to use some sort of detergent to reduce the surface tension of the water bubbles. 

 

You make some good points.

 

I never thought before about an aerocloner being a good benchmark.  I don't use a chiller in my aerocloner.  A few months ago I let a friend (an accomplished soil grower) borrow a homemade aerocloner I wasn't using.  He started cuttings the same day I started some in my ez cloner.  They were of the same strain.  He called me after three weeks and asked me to come check out his clones because none had rooted.  All of mine had already been moved out of the cloner.  It turns out, he had a chiller running with the cloner and was keeping water at 66 degrees.

 

Regarding the detergent, I don't know why I never thought about that.  I've noticed that using Hygrozyme results in a detergent-like scenario of bubbles building up at the surface.  

 

Your point about the bubbles moving the water causing more DO as opposed to the bubbles themselves is exactly my concern with the oxydoser.  I've experimented with using no airstones and the air hoses just pumping straight to the water, creating few but big bubbles that really move the water around.  I saw no difference between that and airstones as far as plant health. I was too timid to continue though, and went back to what always worked - airstones.

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The airlift pump design really supercharges the DO, check out some basic designs here:

 

http://www2.ca.uky.edu/wkrec/AirliftPumps.htm

 

Using an airlift in the reservoir, plus some basic water pump design to recirculate the solution to the plant sites (continuous drip is super easy, and probably what I'd use) would likely be a winning combination.

 

Interesting.  This looks a lot like the GH Waterfarm method.  I used Waterfarms (and homemade equivalents) before I ran DWC.  I wondered why I was getting root rot in DWC and never that that issue with the Waterfarms.  I didn't know how efficient the Waterfarm approach was at dissolving oxygen.  What I didn't like about Waterfarms was that the air line ran through the grow medium, which made moving plants a real chore.  With my DWC, I run the air line through a hole in the top of the bucket, so there is nothing attached to the lid and plants are moved easily.  The same could be done with the air lift pump design.

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They are claiming some incredible water moving efficiency.   They first paragraph of the article states..

 

it was calculated that a 1.0-horsepower (0.75 kw) centrifugal blower could pump 3107 ± 75 (SD) L/min water by combining the individual outputs of twenty-eight 7.6-cm diameter airlift pumps.

 

that translates to 800 gallons per minute (48,000 gph) with 750 watts of power.   A typical submersible hydroponic recirculating pump does 800 gph and uses 50 watts.   That makes the airlift 4 times more efficient.   As a caveat there is a bit of a fudge here in that the air pump lifted the water approx. 32 inches where as the 50 watt water pump is usually rated around 10 feet.  

The airlift pump design really supercharges the DO, check out some basic designs here:

 

http://www2.ca.uky.edu/wkrec/AirliftPumps.htm

 

Using an airlift in the reservoir, plus some basic water pump design to recirculate the solution to the plant sites (continuous drip is super easy, and probably what I'd use) would likely be a winning combination.

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1. How much of a role does water temperature have on root rot? Does the 14% drop in DO from 68F to 82F mean the difference between healthy and nearly dead plants due to oxygen deprivation?

2. - or does the elevated temperature and lower DO simply provide the necessary environment for the bad bacteria to take over?

3. If "yes" to no. 2, can you maintain plant life with nute temps at 82 degrees by using enzyme and beneficial bacteria additives.

All in all, I'm trying to figure out the most efficient (time and cost) way to balance chilling water/aerating water/using additives.

1. Temp has a significant roll in phythium as well as stress and environmentals. The drop in DO means the plants are going to be hunting for oxygen also creating stress and making them more susceptible to pythium and death. (Look what happens when and air stone goes out in a single dwc bucket, but with rdwc you have a better chance staying alive due to the river like effect of the constantly moving water picking up O2). Look at a mangrove, their roots are submerged in water but they have adapted to grow literally snorkels to the surface in order to get O2 to the root zone.

2. It is a catalyst yes.

3. I have ran benies and teas in rdwc more work, you are getting into a little more organic Nutes then. A lot of commercial Nutes DO NOT work well in rdwc and with certain benies and will suffocate the roots and kill your plants or leave you with a lackluster finished product.

 

Hydro in the winter if usually fine up here, in the summer is where the problems pop up. I'd personally never let my water get above 66-68. Anything over 76 and you are hitting the danger zone if you will. Rhizospheres are typically cooler than air temp. Stick your hand in some dirt in a flower bed, it is always cooler than the air temp.

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1. Temp has a significant roll in phythium as well as stress and environmentals. The drop in DO means the plants are going to be hunting for oxygen also creating stress and making them more susceptible to pythium and death. (Look what happens when and air stone goes out in a single dwc bucket, but with rdwc you have a better chance staying alive due to the river like effect of the constantly moving water picking up O2). Look at a mangrove, their roots are submerged in water but they have adapted to grow literally snorkels to the surface in order to get O2 to the root zone.

2. It is a catalyst yes.

3. I have ran benies and teas in rdwc more work, you are getting into a little more organic Nutes then. A lot of commercial Nutes DO NOT work well in rdwc and with certain benies and will suffocate the roots and kill your plants or leave you with a lackluster finished product.

 

Hydro in the winter if usually fine up here, in the summer is where the problems pop up. I'd personally never let my water get above 66-68. Anything over 76 and you are hitting the danger zone if you will. Rhizospheres are typically cooler than air temp. Stick your hand in some dirt in a flower bed, it is always cooler than the air temp.

 

Do you think the difference in temperature between the rhizosphere and the "atmosphere" plays a factor?  As in, there is an ideal range of temperatures for a rhizosphere and an ideal range for "atmosphere," but the difference in temperature between the two makes a difference?  For example, "You always want the rhizosphere cooler than the atmosphere?"

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1. Yes

2. Yes, yes

3. Yes

 

The rhizosphere will pretty much remain consistent outdoors. Indoors since the pot is above ground the pot will get warmer than in ground obviously. The ground close to the surface might fluctuate slightly but the deeper you go the more constant it is. Anything more than a 1 degree switch with effect how the roots uptake Nutes water etc. Need a proper enviro above and below ground. Plant is doing the opposite above and below at the same time. It is like the shirts people wear with a tree and is shows the root zone and it almost mirrors the tree. Like when running aeroponics, the roots aren't submerged in water you are creating a high humidity enviro that is making up for the lack of a substrate or being submerged in water. While your topside is at a higher temp with lower humidity. My pics come out as thumbnails but this is a stem crosssection under an electron microscope. Forgot to add the pic.

post-37430-0-22082700-1490996309_thumb.jpg

Edited by Scarlet_Begonias

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1. Yes

2. Yes, yes

3. Yes

 

The rhizosphere will pretty much remain consistent outdoors. Indoors since the pot is above ground the pot will get warmer than in ground obviously. The ground close to the surface might fluctuate slightly but the deeper you go the more constant it is. Anything more than a 1 degree switch with effect how the roots uptake Nutes water etc. Need a proper enviro above and below ground. Plant is doing the opposite above and below at the same time. It is like the shirts people wear with a tree and is shows the root zone and it almost mirrors the tree. Like when running aeroponics, the roots aren't submerged in water you are creating a high humidity enviro that is making up for the lack of a substrate or being submerged in water. While your topside is at a higher temp with lower humidity. My pics come out as thumbnails but this is a stem crosssection under an electron microscope. Forgot to add the pic.

 

Plant physiology is fascinating stuff.

 

I wonder if the temp difference above and below ground plays a part in the plant's ability to transport water/nutrients throughout the plant...kinda like how maple trees in the spring draw sap up from the roots during the day and send it back down at night, and this activity depends on day vs. night temperature swings.

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The cohesion tension theory is introduced by Dixon and Joly in 1894, which is also known as “Suction due to transpiration”. Basically this theory explains the ascent of sap.


As per this theory there are two essential characteristics of the plant:


  1. Cohesion theory
  2. Transpiration pull

As per the cohesion theory, the similar molecules of water possess the attraction force that is very high more than 1000 atmosphere, this attraction force is known as cohesion force that helps in the transportation of water molecules towards the tip of the plant.


There is also an attraction between the water molecule and the inner wall of xylem.


The upward transportation of water molecules is basically due to the process of transcription where one molecule of water is evaporated and other molecule of water is pulled towards the arial part of the plant by the process of cohesion.


By this whole process of water lifting, the negative tension is occurred from the aerial parts to the base of the plant.


Due to this there is a continuous movement of water molecules in the opposite direction of the negative tension, which is known as the transpiration pull.


This process of cohesion and transpiration pull supports the movement of water channel towards the aerial part of the plant by opposing the gravitational force.


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Then you have your basic root pressure where the weight of the liquid (DWC), or the soil, on the root system, is greater than atmospheric pressure on the upper part of the plant causing a squeezing of the liquid in the roots up the plant. It forces the nute solution into and up the plant. 

Edited by Restorium2

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