I just found a new aquarium association in my area (yay! ) and they had some interesting links on their page, including this one. It's a bit more complex than anything I need for my tanks, but could be useful to anyone with heavily planted tanks. Apparently it's a downloadable tool that helps calculate things like CO2 requirements.

http://www.csd.net/~cgadd/aqua/art_plant_aquacalc.htm

Sweet Fancy Moses! Chuck's done his homework. Looking forward to using it as needed. Thanks for the head's up Chrissy Bee.