So this has happened now almost every time I've brewed, including the current batch I have going - I'll pitch the yeast and I'll get very nice and very active fermentation that slows down in about 4 days. Then after about 10 days I start to see little bubbles that come up from the trub (I use a glass carboy). I wasn't able to know for sure if the fermentation was done (just got a refractometer a couple days ago) so to be safe I let it hang out for another week. Now a full 3 weeks later it is going WILD, like how it did in the first 3 days of fermenting. Ok now before someone says "CO2 release", I mentioned I just got a refractometer and I took a gravity reading 2 days ago which was 1.027 (uncorrected because I didn't have the OG but that shouldn't matter for my purposes) and today the reading is 1.024. The refractometer was freshly calibrated before each use. Is it possible that fermentation just randomly started up again? And why is this happening for my fermentations just about every time?