lighting and CO2 injection?

[Australian natives]

so for my tank (around 55g), i currently have a 4ft light (with a very old growlux bulb). and i have just stumbled apon a working 2ft and 4ft fixture (both with space for 2 globes) and i have decided that instead of getting a new globe for my old fixture, i am goign to get either the 2 or 4 foot lights running.
however, how can i find out the wattage of these fixtures? or should i just assume that it is 40 watts for each 4 foot globe and 20 for each 2 foot? (as my dad suggests).

also, i am assembling a CO2 reactor to go with it, and was wondering if u guys can suggest any precautions i can take to ensure my tank doesn't have a pH crash =P. should i start out with a small amount of yeast and sugar so C02 build up is slow maybe? or should i just not put a reactor in so the bubbles reach the surface quicker?

(im taking a water sample to LFS to get a hardness test as i dont have the kit for that, ill post the results when i get them. although i think it will be soft as i use rain water, which comes from a concrete water tank.)

[rich311k]

10 watts a foot is about right for standard flourscent tube.

You will not over dose CO2 with a DIY in a 55 gallon tank unless you hook up twenty bottles. It is not the PH that is a problem anyway it is high levels of CO2 in the water which cause the fish to be unable to release the CO2 in their blood streams. It will not happen with a few bottles of yeast sugar mix.

[Australian natives]

oh ok =]. fantastic =D.
i shall get to work constructing them then =P. using mountain dew bottles so they are the same color as m ehiem, can i get green airline from pet shops do u think? or will i have to go to a hardware store or something?