Hi. I started an imperial stout on saturday OG 1113 and used 2 packs of Mangrove Jack's M42 pitched at 20C and fermenting at a controlled 18C.
Did not take off as I expected but by Tuesday morning reading 1070.
Will leave it for a couple of days and re test but activity from blow off tube has almost stopped.
Any suggestions welcome.
If your OG was 1113 and your Tuesday morning reading was 1070, your beer is fermenting. My hypothesis given your posting in a beginner forum (no insult intended) is you severely underpitched the yeast and then it ran out of oxygen. High gravity fermentations are tough, even for experienced homebrewers. I understand the desire to do difficult beers but you picked a doozy! Fermenting an Imperial anything:
1. Grow a very big starter of alcohol tolerant yeast, as in make a beer at around 1045-1050, lightly hopped, and use all the yeast from it to ferment the beer.
2. Oxygenate, not aerate, the wort before pitching.
3. Oxygenate it again after about 18 hours.
4. Keep the temperature cool through about half the fermentation to control fusel alcohols.
5. After half the fermentation, let the temperature rise to dry the beer out as much as possible.
6. Swirl the trub up every day or so to keep the yeast suspended.
7. If your yeast gives up, use a high-gravity yeast such as champagne yeast to complete the fermentation.
8. Let the beer age to smooth out the inevitable harsh flavors.
Your post was a bit vague so if you did any of these things and I missed it, I apologize.