I'm brewing my first Russian Imperial Stout. It has been fermenting for 19 days, but it is not quite done yet. It is at 1.042, and the recipe suggested a FG of 1.030 (using Wyeast 1084 or 1056). The OG was 1.110. I used WLP028 that I harvested from a previous batch, about half of the yeast, and saved the rest. It was used the day after I harvested it. Fermentation started in about 24 hours, at a controlled temp of 69°F, later raised to 71°F. I used a blow off tube for the first time so I'm not sure how vigorous it was compared to previous batches.
Should I keep waiting? Add some more yeast that I saved from the harvesting, now about 3 weeks old? If so how much? Thanks for any help.