Nitrites dropped again

Numbers

Date	GH	KH	pH	NO2	NO3	NH3/NH4	Temp °C
5-May-2016	180	80	6.5	0	20	0.50	19°

Observations

• The temperature outside dropped last night. A window was left open, which resulted in a wilting crop. As the room temperature increased, they have started to recover. 
• The water temperature of the tank also dropped to 19º C while the tank heater was struggling, and failing, to maintain a proper range. According to my thermometer, and other reading, it's two degrees below the minimum range for the basic fish I want it to hold. When water's makeup does become habitable for fish, I additionally want to insure it will be warm enough for them.
• The nitrites dropped to zero while all other values, excepting tank temperature, remained constant.
• I see additional growth in the other areas today in the thyme and cilantro areas.

Cycling thoughts

From what I understand, a spike in nitrites should be followed by a spike in nitrates as well as a drop in ammonia. Today's test showed no nitrites, but a constant level of nitrates and ammonia. Should I assume that a delay would exist between the drop of one and the spike of the other?

It's a little puzzling to me that the ammonia levels have not dropped; that no bacteria have developed to convert it into nitrites. I understand that the creation of bacteria for this first step should naturally appear. Perhaps I'm being too impatient?

Nitrobacteria and pH

I recently read on Wikipedia about Nitrobacteria where it thrives in water having a pH between 7.3 and 7.5. When I started the tank, it had a pH of 7.0. As it's been running over the past week or so, it reduced to 6.5. Based on a segment about the Nitrogen Cycle on Backyard Aquaponics site, I could add some calcium carbonate to the water and have some media in the tank for it to attach. If I do this, it would raise the pH, which would create better conditions for the bacteria to thrive. It's my hope that this increase would feed on the ammonia to kickstart the conversion process. The lower pH may be slowing the cycling process. How much to add without increasing it too much? I'll have to do my research.