According to the manual, the Flow Adjustment Knob is the dial that is on the lower left of the unit. Turning down the flow rate on the unit will supply less CO2 to the water, meaning that it "won't be working as hard" to lower the pH. For any pool equipment, a good rule of thumb is to make small adjustments, and then check the water in 24-48 hours to measure the result. A good pH range is typically 7.2-7.8.