The bubbles issue I think is not a problem as they don't form constantly in a stream or something like that. On the other hand the liquid voyancy is not a rapid changing thing. It will take hours for the yeast to do their business before it changes in a detectable way, therefore a bubble here and there will not affect the results I guess. If a bubble appears then you get a way off reading and you just need to way for a bit and take another reading. The soft can take care of that. A very slow changing parameter is being meassured therefore rapid changes will be noise and can be discarded.