A bit different DiY CO2 System - The Planted Tank Forum
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post #1 of 82 (permalink) Old 05-31-2016, 05:19 PM Thread Starter
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A bit different DiY CO2 System

MCSLABS posted a very interesting DIY CO2 system that could be shut off at night, and that has had me thinking about how I would do this if I wanted to try it. My goal would be, as his was, to be able to shut off the CO2 at night, but also to try to make the bubble rate be more consistent between recharges of the yeast/sugar mixtures. Here is what I have come up with:



How it works:
The yeast/sugar/water generates CO2, probably at a rate of about 1 bubble per second. If the solenoid valve is open the CO2 goes directly to the bubble counter and to the tank. If the solenoid valve is closed the CO2 goes to the storage bottle, displacing some of the water in that bottle which goes to the pressurizing bottle. After a few hours enough water is displaced into the pressurizing bottle to compress the trapped air there and that pressurizes the storage bottle and the yeast/sugar/water bottle. To calculate how much pressure is there, assume each CO2 bubble is about 1/16 inch in diameter. So the volume of gas in that bubble is 4/3 x pi x the bubble radius cubed, which is .002 ml. If the solenoid is closed for 16 hours, that is 57600 seconds. The total CO2 generated in that time would be 57600 times .002 ml per bubble, or 115 ml. In a 1 liter bottle that would change the water level by less than 10%., generating less than 1 inch of water pressure - a very low pressure.

When the solenoid opens that will dump all of the CO2 into the tank, at a rate determined by the resistance to flow through the diffuser used. The pressure is so low, just barely above atmospheric pressure which is about 360 inches of water, that a metering valve may not be needed. If the bubble rate is 2 bubbles per second the storage bottle will not completely empty in 8 hours. This would cause the storage bottle to accumulate more and more CO2 from day to day, until the generated CO2 drops below 1 bubble per second. Some experimenting will be needed to determine if a metering valve is necessary.

An added benefit of shutting off the CO2 when the lights are off is that the time each charge of the yeast/sugar/water bottle will last should be three times longer assuming an 8 hour photoperiod.

MCSLABS, do you think this will work? And, is it much different from your system.

Illustration changed to add needle valve and change storage set-up
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Last edited by Hoppy; 06-01-2016 at 04:29 PM. Reason: Modified illustration
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post #2 of 82 (permalink) Old 05-31-2016, 05:46 PM
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Quote:
Originally Posted by Hoppy View Post
MCSLABS posted a very interesting DIY CO2 system that could be shut off at night, and that has had me thinking about how I would do this if I wanted to try it. My goal would be, as his was, to be able to shut off the CO2 at night, but also to try to make the bubble rate be more consistent between recharges of the yeast/sugar mixtures. Here is what I have come up with:



How it works:
The yeast/sugar/water generates CO2, probably at a rate of about 1 bubble per second. If the solenoid valve is open the CO2 goes directly to the bubble counter and to the tank. If the solenoid valve is closed the CO2 goes to the storage bottle, displacing some of the water in that bottle which goes to the pressurizing bottle. After a few hours enough water is displaced into the pressurizing bottle to compress the trapped air there and that pressurizes the storage bottle and the yeast/sugar/water bottle. To calculate how much pressure is there, assume each CO2 bubble is about 1/16 inch in diameter. So the volume of gas in that bubble is 4/3 x pi x the bubble radius cubed, which is .002 ml. If the solenoid is closed for 16 hours, that is 57600 seconds. The total CO2 generated in that time would be 57600 times .002 ml per bubble, or 115 ml. In a 1 liter bottle that would change the water level by less than 10%., generating less than 1 inch of water pressure - a very low pressure.

When the solenoid opens that will dump all of the CO2 into the tank, at a rate determined by the resistance to flow through the diffuser used. The pressure is so low, just barely above atmospheric pressure which is about 360 inches of water, that a metering valve may not be needed. If the bubble rate is 2 bubbles per second the storage bottle will not completely empty in 8 hours. This would cause the storage bottle to accumulate more and more CO2 from day to day, until the generated CO2 drops below 1 bubble per second. A second bubble counter may be needed between the yeast/sugar/water bottle and the storage bottle. And some experimenting will be needed to determine if a metering valve is necessary.

An added benefit of shutting off the CO2 when the lights are off is that the time each charge of the yeast/sugar/water bottle will last should be three times longer assuming an 8 hour photoperiod.

MCSLABS, do you think this will work? And, is it much different from your system.
Why bother with this complicated setup? Use the Citric Acid and Baking Soda method and you'll never have to worry about rising pressure when shutting off the CO2 at night plus you get instant CO2 right from the get-go. You'd have a 2 bottle system and just add your solenoid to the setup.

You can check out this thread from where I started to post to get an idea what I was doing:
https://www.plantedtank.net/forums/20...ml#post9204113
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post #3 of 82 (permalink) Old 05-31-2016, 07:01 PM Thread Starter
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Why bother with this complicated setup? Use the Citric Acid and Baking Soda method and you'll never have to worry about rising pressure when shutting off the CO2 at night plus you get instant CO2 right from the get-go. You'd have a 2 bottle system and just add your solenoid to the setup.

You can check out this thread from where I started to post to get an idea what I was doing:
https://www.plantedtank.net/forums/20...ml#post9204113
The citric acid method can get pretty expensive and from everything I have read, it can need recharging more often than this system would. Sugar and yeast are very easy to buy, compared to citric acid. And, I'm not sure the CO2 bubble rate can be kept consistent throughout the life of each charge. Failing to do that opens the door for BBA attacks.
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post #4 of 82 (permalink) Old 05-31-2016, 07:12 PM
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Originally Posted by Hoppy View Post
The citric acid method can get pretty expensive and from everything I have read, it can need recharging more often than this system would. Sugar and yeast are very easy to buy, compared to citric acid. And, I'm not sure the CO2 bubble rate can be kept consistent throughout the life of each charge. Failing to do that opens the door for BBA attacks.
Well, I bought in bulk. Yes in the long run it is more expensive than a pressurized CO2 system, but I don't know how much you spend on yeast and sugar.

Here is baking soda:
http://www.amazon.com/Sodium-Bicarbonate-Highest-Quality-Organic/dp/B005JHGBUM?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00
Here is the citric acid:
http://www.amazon.com/Milliard-Citric-Acid-Pound-NON-GMO/dp/B00EYFKNL8?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
The citric acid is more expensive per pound but should last quite a while.

The bag I got is probably good for like 9 regular cycles (200g each).
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post #5 of 82 (permalink) Old 05-31-2016, 07:36 PM Thread Starter
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I may switch to a citric acid method at some later time, probably when I'm bored with this method.

In case anyone thinks a DIY CO2 system is essentially free, other than the sugar and yeast, I spend about $51 today, just on parts! That is bottle caps, from Ebay, a solenoid valve from Ebay, 5 check valves from US Plastics, a drop checker from Ebay, and a 2 liter bottle of lemon-lime carbonated water - cost not included, and more bottles needed. Put the word "tech" in a planted tank design and the word "cheap" is never again appropriate!
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Last edited by Darkblade48; 06-01-2016 at 08:28 AM. Reason: Please use the edit function for back to back posts
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post #6 of 82 (permalink) Old 06-02-2016, 06:33 PM Thread Starter
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I just realized that you can store CO2 by dissolving it into water - making carbonated water. So, this system can be simplified to:



With the solenoid valve closed the generated CO2 bubbles into the storage bottle, building up the concentration of CO2 in that bottle, since it has nowhere else to go. Assuming that the solenoid will be off for 16 hours a day, and the yeast solution generates one bubble of CO2 per second, each about 1/16 inch in diameter, you could get about 1.8 grams of CO2 per day stored in the bottle. Each bubble would be about 17 cubic millimeter in volume, which is 980 milliliter of CO2 per day. If all of that dissolves into 2 liters of water, that water will contain about 880 ppm of CO2.

If this is used to supply CO2 at 1 bubble per second to the tank, by opening the solenoid valve and adjusting the needle valve, it would be about twice what is needed for the 8 hour day. If the bubble rate is doubled to 2 bubbles per second, it supplies all that the tank needs for one day, so at worst it gives you one more day off each charge of the yeast sugar bottle. But of course the yeast doesn't stop generating CO2 while you are using the stored CO2, so you could get a bit more than 2 bubbles per second if you wanted. At some bubble rate the stored CO2 won't be adequate for maintaining a steady bubble rate.

I think I will try this scheme first!

EDIT: It would also be possible to sit the storage bottle in a pan of water, with a small heater in it, with the heater being powered when the solenoid is open, or when the photoperiod begins. That would increase the delivery rate of the stored CO2.

Hoppy

Last edited by Hoppy; 06-02-2016 at 08:11 PM. Reason: Corrected illustration
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post #7 of 82 (permalink) Old 06-02-2016, 07:06 PM
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This is very intriguing, interested to see how it works.

How did you arrive at 1/16 dia bubbles? Im thinking they are going to be bigger. At least all my DIY set-ups I would say closer to 3/16 - 1/4"

Something else I wonder, are all 1/16" bubbles the same? For example, bubble size is affected by how much resistance is at the diffuser, relative I suppose to how much pressure the system is generating (eg working pressure)

So is a 1/16 bubble with zero resistance (open co2 line with no diffuser) equal to a 1/16 bubble with a diffuser that requires 30 psi to crack? By equal I mean containing the same amount of co2


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post #8 of 82 (permalink) Old 06-02-2016, 07:54 PM Thread Starter
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I am only guessing about the CO2 bubble size, mostly because it will vary considerably. I did it just to get a ballpark estimate on whether it can work or not. I also left out the CO2 exit line from the storage bottle, and corrected that.

I plan to use this with a very simple diffuser in the tank, possibly a piece of bamboo chop stick. The back pressure from this will be very low. I suspect the primary back pressure source will be check valves, which take about 1/2 psi to open. My experience with these has been that they stay shut until the pressure builds up then they burp out a single big bubble and shut again. I'm hoping that by keeping the check valves below the needle valve I can limit that burping, which makes an annoying noise.

It is also very possible I am overlooking something obvious and this won't work at all!

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post #9 of 82 (permalink) Old 06-02-2016, 09:24 PM
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Hoppy, Give it a go, it might work but I don't think it will be dramatically better than an empty buffer tank as you are still just storing over production by compressing the CO2 in the pressurised tank which is what a buffer tank does. I think it will have created a vacuum in this pressurised tank if you ever managed to get it into the condition shown in the second diagram and this would stop the flow. Have a look and Andy the minions system I posted about last month and you will see he has solved this problem, it also increases the amount of water that is displaced (therefore the storage capacity) and regulated the CO2 pressure as well.
I have built one of these and it is working very well, the CO2 flow rate is set by the height of the storage tank and it is very stable. Andy even did the pressure calculation and storage capacity.

https://www.plantedtank.net/forums/20...off-night.html
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post #10 of 82 (permalink) Old 06-02-2016, 09:42 PM
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This may help.

solubility - What is the carbon dioxide content of a soda can or bottle? - Chemistry Stack Exchange


I think either would work but for safety reasons I would put a high cracking pressure check valve on the whole system.
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post #11 of 82 (permalink) Old 06-02-2016, 10:41 PM Thread Starter
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Hoppy, Give it a go, it might work but I don't think it will be dramatically better than an empty buffer tank as you are still just storing over production by compressing the CO2 in the pressurised tank which is what a buffer tank does. I think it will have created a vacuum in this pressurised tank if you ever managed to get it into the condition shown in the second diagram and this would stop the flow. Have a look and Andy the minions system I posted about last month and you will see he has solved this problem, it also increases the amount of water that is displaced (therefore the storage capacity) and regulated the CO2 pressure as well.
I have built one of these and it is working very well, the CO2 flow rate is set by the height of the storage tank and it is very stable. Andy even did the pressure calculation and storage capacity.

https://www.plantedtank.net/forums/20...off-night.html
Very good! I had read this before, but didn't consider how much of the CO2 would be dissolved in the water, thus not occupying any of the "air space" in the bottle. This is all still a little fuzzy in my brain, but it looks like the rise in pressure with this isn't enough to be concerned about. Tomorrow I will probably have another surge of thinking and make more changes to my idea.

Quote:
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This may help.

solubility - What is the carbon dioxide content of a soda can or bottle? - Chemistry Stack Exchange


I think either would work but for safety reasons I would put a high cracking pressure check valve on the whole system.
Thank you! I read a lot of articles on this subject, but this one seems to be the easiest for me to work with. I need to visit the EBAY and see what bargains are possible for a relief valve. Each time I do this I relearn that however cheap one thing is, when you have 10 things it is no longer cheap.

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post #12 of 82 (permalink) Old 06-03-2016, 12:30 AM
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Cheapness is why I went with a sealed air pump in which I drilled a hole in the top and sealed an intake tubing to it. I had the pump, the valves and the check valves on hand. I did purchase the silicone tubing though

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post #13 of 82 (permalink) Old 06-03-2016, 02:23 AM Thread Starter
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Cheapness is why I went with a sealed air pump in which I drilled a hole in the top and sealed an intake tubing to it. I had the pump, the valves and the check valves on hand. I did purchase the silicone tubing though
Ebay does have a CO2 relief valve listed, for about $7 when you add in the shipping. It is a 60 psi relief valve, which would be more than adequate since those carbonated drink 2 liter bottles can hold over 100 psi reliably. But, since the amount of CO2 that will dissolve in water goes up as the pressure goes up, there might not be an overpressure problem. Tomorrow I will see if I can figure it out. I hope someone who has studied this subject more recently will beat me to it though.

I think I will assume the CO2 bubbles are 1/8 inch in diameter instead of 1/16 inch, which means the total amount of CO2 produced to get 1 bubble per second goes up by a factor of 8. That makes the probability of overpressure go up too.
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post #14 of 82 (permalink) Old 06-03-2016, 12:01 PM
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this might help
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post #15 of 82 (permalink) Old 06-03-2016, 04:56 PM Thread Starter
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Storing CO2 by dissolving it into water doesn't seem to be very efficient. The solubility of CO2 in 20 C water is about .9 ml per ml of water, but the same ml of volume without water will store 1 ml of CO2. The solubility of CO2 in water doesn't increase very much for pressures up to a few atmospheres. And, it is much simpler to store the gas undissolved in water.

If the typical 2 liter bottle of yeast/sugar/water will produce one 1/8 inch diameter bubble per second, it is producing about .033 ml of CO2 per second. That is .033 x 3600 or about 120 ml per hour. 2 liters is 2000 ml, so the time required to produce 2 liters of CO2 would be about 2000/120 or 16 hours. If I have the C02 running for 8 hours a day, I will need to store 16 hours of CO2 production per day. Here is my latest version of this system:



The 60 psi relief valve would keep the pressure in the bottle on the right at 60 psi, so all of the bottles would be at 60 psi. Of course all relief valves are notorious for leaking, so the chances of this working for very long aren't very good.

One thing I like about this scheme is that the water in the first bottle displaces the air in the bottle, so after one day the CO2 being stored would be near 100% CO2.

One thing I don't like about it is that if the yeast/sugar/water bottle produces a lot more or less than one bubble per second of CO2 this might not work very well at all. And, using something like 5 bubbles per second going into the tank might make it run out of CO2, or be very hard to maintain a constant.

I plan to make this and set it up on the kitchen counter first to watch how it works. At least it will be a lot of fun.
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