Following the recent ‘re-discovery’ that diffused CO2 bubbles might benefit plants more than using a reactor (thanks to @Xiaozhuang
pointing us to the T Barr study), I decided to try it. It does seem that I can drive CO2 higher (.4 increase in the Ph drop, Kh ~1dKH, pH7.2 drop to 5.4) without affecting the fish. I’m currently awaiting any change in plant performance, but have noticed a drop-off in GSA activity, probably indicative of increased plant performance. However, the purpose of this post is to share a new (to me, anyway) way to diffuse CO2.
Essentially, this is a design for laying tubing on your substrate that acts as a very long CO2 diffuser. I found that creating needle-sized holes in the urethane CO2 tubing I use allows tremendous design flexibility, while delivering minute, ceramic diffuser-sized bubbles throughout the entire tank, from the bottom of the tank. Placing the tubing under the plants allows the bubbles to get hung up in the plants. Very few make it to the surface so, absorption can occur as the bubbles stick to the leaves, which is considered ideal …and there is no swirling haze of bubbles, such as I used to get with an in-line atomizer, to affect the pristine clarity of the water.
My initial design (pictured) which covered about half the tank floor, under the plants, has been replaced with a single line that traverses the back of the tank. I have about 12” of diffusing activity on each end of the three-foot tubing (where the bulk of my stems plants are), with a non-diffuser section in the middle. The pinholes are spread along these two 12” sections at each end and there are about 3-6 holes in any given inch of these tubing sections.
The holes can be bunched in small sections of the tube for different effects and, being a tube, you can serpentine it anywhere along your floor. An additional benefit seems to be that water can not enter these pinholes when the CO2 is off. This means that check valves may not be necessary or, at least, no more worry about their failure.
To make the minute holes, I use pliers to push a small needle through the sides of the tubing. I use urethane tubing (Clippard .250” OD) and I think CO2-type tubing is necessary given the much greater wall thickness of this type of tubing. Thinner tubing, such as silicone tubing, would likely allow much larger bubbles through the holes.
You will need the pressure from a pressurized system to push the CO2 through these holes. The pressure needed is a function of the number of holes and the bubble size. If pressure is too high, the bubbles are large enough to immediately rise to the surface where they do not get absorbed well. For example; right now I have a three-foot length of tubing laid along the back of the tank substrate. Many holes are in the first foot and the last foot (nothing in the center). Given the number of holes I have, I am sustaining about 35 ppm of CO2 with 15 psi in a 29-gal tank.
To plug the end of the tube, I use a plug for drip irrigation (Rainbird – 30 of them for $7 on Amazon), but you might be able to melt the tube end closed. I also use drip irrigation parts for the various “T”, right-angle and other connectors, as well as the long black tube that runs along the inside corner of the tank top to the substrate where it connects to the main urethane tubing (pictured). The CO2 and drip irrigation tubing comes coiled. To straighten it out, I straightened a wire hanger, inserted it into the tubing and placed it in an oven for 10 minutes at 150F.
The process I use to optimize the bubble size and CO2 ppm is this:
I start with the tubing configuration mentioned above (your design may be different based upon plant layout, tank size, etc.) and about 20-25 psi. I lay this in the front of the tank to observe the bubbles. Usually, it starts by having large bubbles that immediately rise to the surface and are wasted. However, it can take a few hours for the bubble sizing to settle in, so wait at least three hours to see if any changes are needed. The bubbles, ultimately, should be so small that they rise very slowly and are difficult to see from several feet away, much like a ceramic diffuser would create. If you still have large bubbles after three hours, put more holes in the tube. Repeat this process until you have no large bubbles for a day. Then place the tubing where you want it. Now, you can adjust the pressure as you need to reach your CO2 ppm target.