I wish you luck with that recipe. Adding acid blend to a mead before fermentation is asking for trouble as the fermentation can bring the mead down well below the pH at which yeast is comfortable. Coffee is also quite acidic (not sure how acidic it is but it does have a low pH) and using "instant coffee" is going to result in more bitterness than I think you might be expecting. But also the recipe itself is inaccurate. Three pounds of honey dissolved in 7 pints will likely result in a gravity of closer to 1.120 or thereabouts, so the yeast will be under some stress due to the high acidity and relatively high concentration of sugar. Do you have any way of taking a pH reading. You want the pH to be around 3.5 or thereabouts - even without acid blend and the addition of coffee, IMO , mead can drop to 3.0 or lower as there are no buffers in the honey to prevent the fermentation really doing a number on the acid levels. Not certain of the best solution but one thing to do is add a small amount of potassium bicarbonate (or potassium carbonate if you can get that). This will help reduce the acidity and add the potassium that honey often lacks. But of course, the problem may not be connected with the acid level of your must.
What yeast are you using? How old is it? How hot was the water when you pitched the yeast? Did you allow the yeast to sit on top of the must or did you stir it in straightaway without allowing the yeast to reconstitute itself?
