After making my stir plate, I did my first starter with a WLP 400 Belgian Wit yeast. I made a 1500ml starter (using yeastcalc.com), used a 3000 ml flask, and the first starter went fine. Chilled overnight and decanted, added another 1500ml starter for stepping up, and now I have yeast gushing out of the top of my flask! I would have thought I had plenty of head space, but apparently not. Is this normal? Recommendations?