I brewed on friday hit my OG pitched my (no starter) white labs London ale yeast and everything went as planned. Sunday it was bubbleing and building krausen as usual. Well I checked it on Monday and the bubbleing had stopped and the tiny bit of krausen had started dropping. I checked my gravity and was no where near the set FG so i fear I have stalled. Should I pitch more yeast? If so, more liquid of the same or a cheaper dry to re-activate?