Acid and Base Yeast Lab

In the acid base lab, my partner and I had hypothesized that the acid would create the best reaction because in our elephant toothpaste lab, the hydrogen peroxide had produced a large reaction with the hydrogen peroxide, which had a pH level of 2.6. We had assumed that if the lower pH of the hydrogen peroxide had caused a reaction, so would the low pH of the diet cola, which had a pH of 2.9. However, we had been proved greatly wrong. Our results are available below:

The green was the antacid (base), the blue was the skim milk (neutral), and the cola was red (acid). The acid had the greatest initial rise, but the slope soon lowered. All of the tested materials didn't have a steady rise, they all had steep slopes and some more level slopes. Our hypothesis had been proved wrong  right after we had conducted our first test and found that the neutral skim milk had produced more gas than the acid. At the end of all the tests, all of the pressure levels were on the rise, but we had to keep the time as a constant (and the lab wouldn't let us go longer), so we stopped at 2 minutes. Our group had noticed differing pressures and results from other groups. For example, one group had acid as the highest with a pressure of 140, but upon closer investigation, we discovered that the groups who we noticed differences with had added more hydrogen peroxide or more yeast than necessary.