Y'know, I've been thinking. I also make wine, and to keep the yeast going with many recipes you have to add a nutrient. Most of our DIY CO2 recipes don't include a nutrient. I wonder if a wine yeast plus a nutrient from the winemaking shop might give a much longer lasting mix - I'm currently connected to a pear and plum wine (I combine my DIY CO2 with my DIY wine), and it's producing around 80bpm and should be expected to ferment for around a couple of months or more.