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The results are IN!
PH 6.2
PPM 820
Measured in mg/l
DO levels at 67F:
Air stones: 8.0
Ventruri: 8.0
Water fall: 8.1
Flooming: 7.9
CapnStyle: 8.1
All at the same time: 8.2
DO levels at 78F:
Air stones: 7.2
Ventruri: 7.2
Water fall: 7.3
Flooming: 7.1
CapnStyle: 7.3
All at the same time: 7.4
I also tried adding 5ml/gal of H2O2 at the request of sky in the warm water. This raised the DO to 7.6. Still, not even close to the DO levels in cooler water. 10 hours later I checked it again, and the DO was back down to 7.4 H2O2 is not a good solution.
My hopes are crushed. I was hoping there would be a technique that would compensate for high water temps. If you have warm water, can you add more air to compensate? Nope. Take a look at the numbers. No matter how much air you add, you can't get DO levels past their saturation point.
It's all about temp. I don't care if you if you use 100 airstones or a hot tub venturi, water has a certain oxygen saturation point, at a certain temperature, and you can't get it any higher. All of the methods are acceptable methods. It is not possible to compensate for higher temps, by putting in more air.
Here's how I tested. I used the same 27gal container of water, with 15 gallons of water in it. After introducing each method, I waited 15 minutes before taking a measurement. When taking the measurement, I waited 5 minutes for the meter to settle to ensure an accurate reading. Then I waited another minute to make sure the reading was accurate.
I tested one of my reservoirs from an experimental grow method I am doing, which has roots sitting in water (sort of like DWC) with two large air stones. Water temp at 72. The DO was 7.6 Then I unplugged the air pump. Within 30 minutes, the DO was down to 5.4. That's REALLY low.... proving my previously made statement that DWC requires a battery back up power supply. When I turned off the air to an empty res (with no roots in it) the DO level also dropped, but not as fast as it did with roots. The roots are using up oxygen for sure. This explains why the root zone can quickly get funky and root rot and set in so quickly.
The good news is we did learn a few things from this experiment.
If you are growing DWC or any grow method where roots sit in water:
1. Aerate your reservoir. It doesn't matter which method you choose, they all work well.
2. When there is no water movement, DO levels drop significantly. For example, if you put an air stone in one side of your res, and you have no other water movement, the DO on the other side is a little lower. If you're using air stones, you should have bubbles covering the complete surface.
3. If you can run a water pump 24/7, do it. Water circulating and breaking the surface works great, and pushes that nice oxygen saturated water around your root zone. This is one of the reasons undercurrent and bio buckets work very well... high water flow.
4. Flooming was the worst results, but it is true what they say. Simply moving water at the surface does oxygenate the water. However, I tried another test, not listed above, where I floomed so much it created a mini geyser, like godzilla emerging from the ocean. This method worked just as well as any other method, however it is inconsistent, depending on the water level in the res.
5. You can see from the results, the methods where we break the water surface, (Capn style and waterfall) provided the best DO levels, even better than the 4 giant air stones and a $65 gen hydro air pump. Albeit marginal, it does show proof that breaking the surface is the most effective.
6. Personally, I still like the Capn Style method best. It shows one of the best DO levels, plus allows you to run less water in your res, so your roots are wet but not submerged (as in aero). Roots won't dry out, water is circulated constantly.
7. Unfortunately, any method that requires a water pump to run, requires a chiller (unless you have a magical way of keeping the water cool). Even the small water pump increases the temp of the water by 3-5 degrees.
8. Any method that has roots dangling in water, should have a backup battery supply.