BTW, I've read this newsgroups, several websites and a few other
newsgroups and there's so many diferent opinion about this that I
don't know...: Is CO2 really a necessity in a tank if I want to
maintain plants

It depends what plants you want to keep. Once you decide on the plants you
like you find out wheather they will require high or medium light. If you need
high light (above 2 wpg) you will also need CO2. If you only have low to
medium light plants (1.5 - 2 wpg) they don't need the extra CO2 to do well.
Some of them won't grow as fast without the extra light and CO2, but that can
be a plus too if you don't want to be constantly trimming them.

It's all a balancing act with the CO2, light, and nutrients. The plants won't
do well if there is too or too little of any one of these parameters.

One more thing - ammonia is poisonous to plants as well as the fish. The
plants can only utilize ammonium, nitrites and nitrates.

Good luck
Cris