I brewed a Black IPA O.G. 1.067 on Monday (4 days ago). The first evidence of Krausen forming was about 20 hours after pitching. The fermentation soon after got up to a nice active level in terms of bubble frequency, however I was always concerned because the Krausen never grew to the levels I am used to seeing. At most there was only about 3/4" of Krausen during peak fermentation. Also, approximately 42 hours into fermentation, I came home to find that the temperature had risen to 79F. I quickly transfered the carboy to a swamp cooler and got the temperature to 68F after a couple of hours.
Concerned with the health of the fermentation and the noticeable drop in activity at day 3, I took a gravity reading of 1.031. Today (day 4), I read it again and it is still at 1.031. It appears stalled at this range. I have 2 variables that were introduced for this brew that I have never dealt with before.
1. Being my first dark beer on my new all-grain system, I tried to adjust the mash pH using baking soda. I have very neutral water here (pH ~5.7) so I used John Palmer's chart for determining pH adjustments. Using the figure below, I determined I needed 270 ppm HCO3. I didn't do my math correctly and only added 3/4 tsp of baking soda (~115 ppm HCO3 in 5.5 gallons of strike water). I also have very low sodium content in my water so I was not worried about adding too much sodium from the baking soda. Could this stuck fermentation be a result of my mash pH being too low?
2. More likely is the fact that I reused two different types of yeast for this brew. I had about 5 oz of California Common that was pulled from a primary cake and refrigerated for 2.5 weeks as well as about 5 oz of a house ale yeast from a local brewery that was also pulled from a primary cake and refrigerated for 1 day. They were brought to room temperature and pitched with no starter into well-aerated wort.