Re: Stuck Fermentation in a cranberry juice mead
I would start by double checking my Sp Gr reading as Yo suggested. Then I would check the label on the juice - make sure it doesn't have any sorbate, benzoate, or anything else listed as preservative that would impair the yeast. If it does, you batch is probably done for.
Next question would be how long did you wait after the campden tablet before pitching the yeast? In a very acidic environment, you will have a lot higher level of free SO2 which could have stalled the yeast. You can get rid of some of the SO2 by keeping the bucket open and aerating the must well - I would beat it silly with a wisk or electric mixer. In the future remember to aerate the must well, as oxygen is important in the initial phases of fermentation to allow the yeast to grow and divide and build cell walls.
If you didn't rehydrate the yeast prior to pitching, I would do so. If you use Go Ferm to rehydrate the Lalvin yeast, you will get them off on the right foot. I would take another packet of D47 and rehydrate it before re-pitching following the manufacturer's instructions. You can use an entire 5 gram packet in a gallon batch - it won't hurt it.
The pH may also be a problem. At 3.0 it may stall the yeast. While I have seen ICV D47 ferment well at 2.9, your best bet would be to raise the pH with some potassium bicarbonate if you can get it. One gram at a time until the ph comes up to 3.5 or so. For future reference, you generally don't need to add acids at the beginning of fermentation, and in fact, it may cause your pH to drop so low that you stall - especially if you are using very acidic fruit. You can add acid after the fermentation is complete and adjust it to your taste.
I hope this is of some help. The wizened masters here may have some other suggestions for you.
Best of Luck!
Lanne pase toujou pi bon
(Past years are always better)