I've gotten a lot finished up in the past three days before I head into spring semester tomorrow. I roughly completed a DIY CO2 injection system for my fish tank today. I'm adding plants back into the aquarium and having a little bit of CO2 might help them out. You can learn a lot more about the concept on John LeVasseur's site. Basically I'm using a yeast culture in a 2liter bottle to produce the CO2 and letting it bubble into my aquarium through an air-stone. So far everything seems to be working out, although I'm only about eight hours into the experiment. I started with a rather high pH of 7.6, I'm hoping to lower this to about 7 using CO2. I've noticed a drop to 7.4 since I took the 7.6 measurement yesterday. I'm hoping this huge swing was just due the the vast water replacement two days ago. I'll check the pH in a few hours and see whats going on.