I too have the milwaulkie set up that some folks are talking about. I also have a 10# CO2 bottle and a pH controller. I bought the regulator and pH controller from
www.aquacave.com. It was very reasonably priced and was at my door 2 days after I ordered it. If you order the regulator set-up with the controller you get a $10 price break. Ends up being about $160-170. The shipping wasn't very expensive either...I spent like 8 bucks including some other stuff in my order. I think that the controller is great. I set a pH value, and the controller makes sure that's what the pH stays at. It does this by turning the CO2 flow off or on. As you add CO2, carbonic acid is disolved into the water, lowering the pH. When it cuts off...the opposite happens. In order to utilize the controller, you must have a solenoid valve. The controller works as a power switch for the solenoid, opening and closing your valve. If you set your kH to a known level, then it is very easy to regulate your CO2 ppm. A KH of 4 with a pH of 6.8 set on the controller will give you good results. The system is extremely simple. I got my regulator set up, called around, got a filled 10# bottle for $56, then went home. The regulator assembly simply screws on to the threaded portion of the bottle. If you plan on using the pH controller, plug it in, set your desired pH, throw the electrode into the tank, and plug the regulator solenoid into the pH controller. Make sure your bottle is open, set your regulated pressure to about 10-20 psi and attach your CO2 tubing to your reactor...it's a piece of cake. I think you'll be much less intimidated once you see everything in front of you.
As far as water changes and such, I think the pH controller makes it pretty easy. Just add your dechlorinated tap water and let the controller adjust your pH to the set pH value. After water changes, you will have to double check you KH and make sure it is still aroud 4 degrees (or what ever you decide). By maintaining KH and pH, the proper amount of CO2 will stay constant.
If your power goes out, the only thing that would happen, if you were using a controller, is the CO2 supply would shut off. If this happens it's no big deal. Unless you have a really big gas off through water turbulence, in which case your pH would start to rise. I wouldn't expect a big pH swing otherwise.
To regulate CO2 concentrations without the controller, you have to use the chart Joe gave you. Get a pH reading, get a KH reading, and see where they intersect on the chart. For example, if your KH is 3 degrees and your pH is 6.6, then your CO2 ppm is 23. 20-25 ppm is a good amount that will be great for your plants and won't suffocate your fish. Hypothetically, say you test your water and you have a KH of 4 and your pH is 7.5. You'd want to decrease your pH by adding more CO2 to get a desireable CO2 ppm. So you would increase the rate of CO2 entering the tank. As this happend, carbonic acid is dissolved and pH goes down. Without a controller...YOU MUST BE CAREFULL!!! if you set your CO2 rate too high, too much carbonic acid could be dissolved in the tank and will result in a drastic plumet in pH. This will probably kill your fish through shock or CO2 suffocation. When you make changes, do so VERY gradually. This is why I like my pH controller. I can set the CO2 rate pretty high and not have to worry about it. When the water's pH hits 6.8, the controller shuts off the CO2 flow until the pH is above 6.8 again. On that same CO2 page there is a calculator that figures out the CO2 concentration for you...just fill in the blanks with your water parameters after KH and pH and it will tell you what you CO2 ppm is. P.S. once you enter the values for kh and pH, the CO2 concentration doesn't show up until you click out of the last field you entered in.
Without the controller, you will eventually find a rate that will result in a constant pH. A balance will exist between the co2 entering the tank vs being gassed off.
I know this may sound a bit technical and all, but it is very very simple. If you have any questions, feel free to keep on asking.
-Jamie
