I'm doing six 3L fermentation trials for mead right now, comparing different strains, trying my hand at Curt Stock's Even-speed-mead method, and also the effect of very hard water on mead. I'll do a more detailed write-up later, but the initial results were shocking.
OG: 1.050
500g honey
2g yeast (properly rehydrated)
A1 - 71B with hard water (400ppm CaCO3)
A2 - 71B with lime-softened water (50ppm CaCO3)
Day 0
Added 0.65g Fermaid K to both
Added 0.30g DAP
A1 pH - 5.9
A2 pH - 5.8
Day 1
Roused
Day 2 - SG: 1.030
Roused
Added 0.65g Fermaid
Added 0.30g DAP
A1 pH - 2.3. Added 1tbsp+1/2tsp of 5% calcium hydroxide solution, which raised the pH to 3.7
A2 pH - 1.8. Added 3tbsp of 5% lime solution, which raised the pH to 3.8
I degassed the samples by shaking them repeatedly in a mason jar, and also by letting them sit out for a few hours. I calibrated my pH meter was calibrated twice, to 7 and 4, because I didn't believe my results.
I really didn't expect the pH to fall that much that quickly. I'm not surprised at all that most mead fermentations take months to finish, since the must becomes so hostile to yeast so quickly.