fermenting a bochet, I dropped a bluetooth hydrometer in the must and started with a gravity reading of 1.128. Pitched lalvin EC-1118, and over a day the gravity has gone up to 1.144. I've heard that if your yeast is active enough, it can physically push your hydrometer up, and throw your reading off. However, would that not mean that I should have some visible airlock activity?
I'm also quite sure my airlock is working properly - the fermenter is a corny keg, so when I pull the pressure valve on the lid I can see the fluid level in the airlock drop. If I remove the airlock and push it on again, I can see it start at a higher level, and pull the pressure valve, I can watch it again.
what could cause this?