Originally Posted by irishwater
First off, a low FG is a good thing...
If your OG was 42 (1.042) then your FG should be in the 11 (1.011)neighborhood.
If it's still at 30 then I'd say it's stuck or you didn't aerate it enough. Since it's already started fermenting you don't want to aerate it, but you can add more REHYDRATED yeast. Boil up a cup or two of water, cool it to warm then mix in the yeast and let sit for 15 mins...add to the fermenter, recap.