I would sometime
succesfully reduce the PH around 7.5, but less than 24 hours latter it
was back up to 8+.

That's a fairly common experience, even in unplanted tanks. It's not easy to
permanently change the pH of a tank.

Do you know what the pH of your tapwater is? Measure it after letting it sit
out in a cup overnight. Or after aerating it with an airstone for 20 minutes.

Is CO2 really a necessity in a tank if I want to
maintain plants?

No. It's only necessary for high-light tanks. If you keep your lighting
around 2 wpg and have plenty of aeration, CO2 isn't necessary. If you go above
3 wpg, it *is* necessary.


Leigh

http://www.fortunecity.com/lavender/halloween/881/