The more headspace the more breathing because it's mainly the gas above the liquid that is changing it's density with temperature. This can cause suck-back of liquid in the airlock.You are right on.. I have had some pretty big swings in temperature in my apartment lately.. It was about 60 in there yesterday.. and a lot of the vodka was sucking back into the carboy.
I think that in the future just to be on the safe side, when I do a Belgian again, Im going to buy a 5 gallon carboy.
For now I'll wait and see if this stuff spreads.. if I get a white layer all the way across I'll know its and infection.. if not, I'll bottle it in a couple weeks.
Dry hopping takes better to a tripel better than it does to a dubbel, but these days just about anything goes.The spots are smaller than that.. maybe an 1/8 of an inch, but they weren't there before. I didn't dry hop it.. actually I've never heard of dry hopping a Dubbel or Tripel