Carboy airspace levels?

[blairellis]

How much airspace do you need to leave for proper fermentation in a 6 gal carboy?

 

[Nateo]

Depends on your yeast, and if you're using a blowoff tube. I use 25% as a rule of thumb, but I'll bump that up to 30-40% if I'm using 3787 or others that krausen really hard.