i've done 4 batches one month ago, one per day, day after day. My batches now are of 60L, and I use 2 30L fermenters for each batch. 2 of the 4 batches are the "same recipe", so I have 4 fermenters ...
EDIT: I see from this post and from elsewhere on the Web that a bubbling airlock is apparently not an indicator for fermentation, as there could be a leaky lid. Regardless, doesn't a non-bubbling ...