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When the yeast feeds on the sugar in the water, CO2, or Carbon Dioxide is produced. The thing about this production is, it just keeps on going! If you were ever to block the flow, trapping the air in the system, pressure will build up until there is an explosion of pop-bottles, or what-have-you. It's important to make sure that the air is always allowed to escape into the aquarium, and that excessive pressure is never allowed to build up.
The second danger is what we call back-siphoning. Some times CO2 production will stop, due to whatever reason, and a vacuum will start to form. This will in turn start to suck the water from your aquarium down into your "generator" bottles, creating a siphon. Then, a lot of times, a leak might form, meaning that by morning, the water from your tank could possibly be all over your floor. To prevent this, ALWAYS use what are called check-valves. These can be purchased at almost any pet shop, and work by only allowing air to flow one way, but not back the other way. So, when in-line with your CO2 tubing, it will let CO2 go into the aquarium, but never allow air, OR water to travel back down the tubing into the system. Infact, you should use these with any air-tubing that could potentially start a siphon. Spend a couple bucks on this, and save a world of trouble from flooding
You'll also want to check your levels now and then, especially when you're first setting up. Too high can hurt the animals, while too low won't help much. Bichirdude has posted a useful chart to find your levels by using KH and pH. Note that things like phosphates will make this test inacurate.
As for tubing, it really depends what you use when it comes to effeciency. Silicone tubing is so permiable (leaky) by CO2 that it could almost be used as a diffuser in a pinch :-P The traditional stiffer tubing is vinyl, by the way. As you can see from the chart, 20,132(silicone) is incredible compared to a mere 360 of vinyl. (The higher the number, the more CO2 is lost)
QUOTE (tubing permiability chart)
FEP @5.9
PTFE @ 6.8
PVC @ 6.8
Nylon @ 20
Viton @ 79
Polypropylene @ 90
Tygon Fuel @ 100
Polyethylene @ 280
Tygon Lab @ 360
Vinyl @ 360
Polyurethane (clear and aqua-tint) @ 395
Norprene @ 1200
Gum Rubber @ 1311
Tygon Pressure @ 2700
Tygon Ultra-chem resistant @ 4840
Silicone @ 20,132
Source: Cole-Parmer Tubing Guide
PTFE @ 6.8
PVC @ 6.8
Nylon @ 20
Viton @ 79
Polypropylene @ 90
Tygon Fuel @ 100
Polyethylene @ 280
Tygon Lab @ 360
Vinyl @ 360
Polyurethane (clear and aqua-tint) @ 395
Norprene @ 1200
Gum Rubber @ 1311
Tygon Pressure @ 2700
Tygon Ultra-chem resistant @ 4840
Silicone @ 20,132
Source: Cole-Parmer Tubing Guide
That all being said, welcome to the world of CO2 injection!
--cich
This post has been edited by cich: 24 October 2005 - 11:37 PM
