So I've got an IIPA with WL Vermont yeast going but activity dropped off really fast after 36 hrs of monster fermentation. I had foam coming out of the blowoff tube yesterday and today there was the barest of bubbling happening. I did a pretty good size starter but am wondering if my calculations were wrong and if i need to pitch more yeast. My LHBS doesn't carry the Vermont yeast so I'd have to either reorder or pitch with S5. The recipe said I could have used either, but I didn't know if it would screw it up to mix yeasts once its already going. Thoughts?