Went away for a couple days and came back and there isnt any activity in my beer kit. It was bubbling before I left. The temperature did get as low as 15 celcius but it sat around 18 celcius for the most part. I had my wife top up the air lock and she may have put too much in, so some sterile qater may have gone in. How do i get it going again? Shake it up? More yeast? Warmer?