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Old 10-12-2005, 01:50 AM   #1
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Problem with my DIY CO2 *updated*

Hi,

I've run my DIY CO2 plan a few times thru this forum, so u may be quite familiar with it. However, I've encountered a problem and would like ur suggestions.

Briefly, this is my DIY CO2 setup:

A 2L Coke bottle as the generator, connect that to a powerhead with a "venturi" input (like the Hagen 20 powerhead), then connect the output of the powerhead to the gravel vac with the sponge at the end of it.


However, I've run into a problem. It seems, that the input of the tubing to the gravel vac is a bit smaller than the output of the powerhead. A picture of what I'm saying is attached to this post.

This has resulted in some backflow of water out of the venturi. The pressure isn't much, and if I hold a piece a 10-15cm piece of airline tubing vertically, the pressure isn't enough to push the water out of the airline tubing. Also, I blew into the airline tubing (not smart, taste of aquarium water ), and bubbles started to develop in the gravel vac (which I'm assuming air is successfully being pushed in)

However, my concern is whether or not the pressure will be strong enough, and also, over time when the output of the generator weakens, whether or not that pressure will be sufficient to introduce CO2 bubbles into the system.

What I'm asking, in your experience, will you think that the pressure from the CO2 generator is enough? If not, I prolly have to think about drilling a bigger hole into the gravel vac so the "connecter tubing" will fit straight into the gravel vac rather than the grav vac's original tubing
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File Type: jpg diy_co2.jpg (12.4 KB, 188 views)
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Old 10-12-2005, 08:49 AM   #2
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OK, you're asking about pressure. I've read posts where people had a clog in the air tubing and the soda bottle popped (pardon the pun), spraying bad malt sludge all over.

the input diameter to the gravel vac should be giving you that much back pressure. I would check the sponge. You want something that will let water flow very quickly through with very open pores.
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Old 10-12-2005, 04:05 PM   #3
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I think it would take a substantial change in size for that to be the cause of all of this. One solution might be to run two bottles and start them a week or two apart. this will give more consistent production.

::EDIT:: In fact, after my initial post above, I re-read your description. The "vacuum" is because your using the powerhead venturi as the input of your CO2. If you instead, drill a hole in the reactor and put your CO2 hopse directly into the reactor you will not have to worry about this issue.
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Old 10-12-2005, 11:06 PM   #4
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Thanks for the replies. I have heard of the popping soda bottle b4, but I forgot to factor in this possible problem. Thanks for reminding me about it, and because of that, it would be right not to risk it.

I think my sponge should be fine. It does let a fair bit of water get through it. It is not something dense like filter floss or anything. It seems quite "hole-y"

Oh yea, I was so tunnel visioned on the venturi I forgot all about adding CO2 directly into the reactor.

For that, I just have to insert the tubing into the reactor don't I?
1. Do I have to worry about adding an airstone to the end of it?
2. Also, should I put a sealant around the drilled hole and the tubing?
3. In which case, what sealant should I be using? Aquarium rated silicon?Superglue?
4. As an alternative, would be it viable to me to just insert the tube from the output area of the reactor and have the end of the tube inside the reactor? (I actually have to ask my mate from work to do the drilling for me , and I only see him twice a week. Itching to get it running asap so looking at an alternative without drilling )


Thanks
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Old 10-12-2005, 11:14 PM   #5
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1. nope, especially if you have stuff in the gravel vac to break up the bubbles.
2. not if the hole is slightly smaller than the tubing, and you squeeze the tubing through.
3. I use superglue as silicone doesnt work for plastic on plastic bonds ime. Superglue gel is known to be safe submerged.
4. probably, but you'll probably need to secure the tubing.

I use venturii injection too (return line) and get a little backflow until the canisters produce gas. Staggering two bottles produces enough stable flow, and I have an on/off valve inline for mix changes. A separator bottle or a check valve ensures no water reaches the canister.
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Old 10-13-2005, 12:28 AM   #6
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1. I don't really have anything in the gravel vac to break it up. I was thinking about bio balls (small ones) but I didn't want to pay the $30 for the pack of them.

4. I'll prolly try this and see, with trial and error, how it goes. If not, I suppose I have to start drilling.

Also, I'm a bit concerned whether or not this backflow could damage the PH. I don't think it should, but leaving open the venturi area to act as a "release valve" would be a sensible precaution, wouldnt it? (As opposed to blocking it off - the pressure should be sufficient to churn up the CO2 bubbles)
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Old 10-13-2005, 12:40 AM   #7
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Anything that's water safe works for breaking up the bubbles. Shotgun wadding is a lot like bioballs and a popular replacement. At your volume I wouldn't be surprised if you get proper ppm without stuff in there.

Remember the venturii attachment is often used to suck in air for oxygenation. The PH will be fine.
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Old 10-13-2005, 01:26 AM   #8
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yep I know its function. I was just concerned about reducing the output cross sectional area (CSA) of the PH (the CSA of the grav vac nozzle is smaller than that of the PH output nozzle CSA). Then again, it should just mean the pressure/"pushing power" of the PH's current should just be slightly greater than it usually is from the reduction in CSA.

I've never heard of shotgun wadding? If it's related to firearms, I most likely won't be able to obtain it where I live, but I am curious to what it is..
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Old 10-13-2005, 04:02 AM   #9
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Here's one type and here's another. They're popular bioball replacements because of their surface area, but again in this application anything water safe works if you need it at all. Just an example.
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Old 10-13-2005, 05:03 AM   #10
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oh ok.

hmmm... what about ceramic rings? or would they be too heavy? Is the idea to have something that will move around in the reactor?
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