Hi everyone

As with many people, my first post here is also one with a question about mead (possibly) gone wrong. I have two batches which I started brewing on 27/04. At that time I did not know this site and I had followed instructions from a book I bought. In that book there was the following recipe:

7 litrers water
6 kg of honey
20 gram of citric acid
4 gram of yeast nutrient
3 gram of yeast

Because these first few tries are mainly for me to learn and to experiment, I split up the amounts in two batches. In on I added the citric acid. In the other I didn't.
What is my problem? We're now 2 and a half week further. The one without the acid is still bubbling. For the past week bubbles come once every 8 to 10 seconds (in the beginning they both were at 3 seconds) (I count every day). The other one (with acid) stopped completely about 10 days ago.
When I take a closer look, I can still see small bubbles coming up the side of the base but much less then in the one without acid.

Further info: the temperature of the room where the mead is, is usually between 20 and 22C (can't get it lower).

My questions:
- is this normal behavior? Is this because of the acid? If yes, what is the process behind it?
If not, what else could be wrong?
- how should I proceed? According to the recipe I should stir after three weeks (about now) and then leave it again for 2 weeks.