Cracking DIY CO2 fittings - The Planted Tank Forum
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post #1 of 6 (permalink) Old 04-10-2011, 01:33 AM Thread Starter
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Cracking DIY CO2 fittings

So I finally decided to go medium tech at least and add a DIY CO2 system. So far everything is working almost perfectly: I'm using a 3 liter bottle with a ceramic diffuser in the back/filter section of a 29 gal Biocube so I don't see the bubbles but seems to work very well as far saturation. Some bubbles float up agianst the current, some get sucked into the pump and blown into the tank. Via my drop checker it's reading a nice pale green, plants are responding well with growth and pearling.

I'm getting about 2 bps on average for about 2 weeks. 1 problem, after about 2 weeks my fitting start to break and crack. I've drilled a 3/8 inch hole in the top of the cap and used a brass bulkhead fitting from Home Depot to make the connection. I've even used silicon around it to make sure it's air tight although doesn't seem necessary at first as the bulk head make a great tight fitting to start. It seems that the pressure and/or the corrosive nature of CO2 is causing the cap to go brittle and crack within 2 weeks though.

Ay suggestions?

thanks in advance
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post #2 of 6 (permalink) Old 04-10-2011, 02:54 AM
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co2 can be really hard on many plastics and can also cause airlines to fail. when i used diy co2 i used a 2g garden pump sprayer for a couple years with no problems. i also had experienced the plastic of the soda bottles failing.
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post #3 of 6 (permalink) Old 04-10-2011, 03:36 AM
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Im a printer and got hold of a couple of these wash up bottles They work perfectly as the tubing just fits onto the nozzle = no leaks or hassles.

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post #4 of 6 (permalink) Old 04-10-2011, 04:19 AM
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i experienced the same thing when i was using DIY. The bottle caps would crack after a few usages specialy the ones in the reactor.
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post #5 of 6 (permalink) Old 04-10-2011, 09:02 AM
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A soda bottle cap is obviously designed to withstand both CO2 and pressure.

I suspect what's really going on here is that when drilling the cap, if the drill bit binds or catches at all instead of cutting smoothly, it creates tiny cracks which radiate out from the hole. Under pressure, these cracks tend to grow. Especially the amount of pressure it takes to drive a glass diffuser, which many people don't recommend using with DIY CO2 at all.

Use a sharp drill bit. Use lubrication, a bit of water is sufficient. Don't force the bit, push gently and let it do the work. Use a drill press if possible, with some scrap wood under the cap. After drilling, you can use a heat gun, flame, or soldering iron to melt the edges of the hole; sealing any cracks enough to keep them from growing.

I have never had a cap fail, or show any signs of failing or becoming brittle. One has been in use for years.

I also don't use glass diffusers with DIY because of the high back pressure. Any failure that causes sudden depressurization will cause the mixture to instantly foam up, like shaking a bottle of soda then opening it; creating a nasty mess. If the sintered glass diffuser element breaks, that mess ends up in your tank.
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post #6 of 6 (permalink) Old 04-10-2011, 11:20 AM Thread Starter
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thanks for the tips. I'll try a different bottle next time and extra careful on the drilling and see if that helps. I am using a second "gas chamber" to protect against foaming but so far no problems there. Really like the ceramic diffuser as it works perfectly in the back of the biocube. If I can't diffuse properly whats the point of doing it at all? was amazed how well it really worked: almost perfect constant levels of CO2 until it cracked
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