You have to find another liquid test kit that reads below 6.
A calibrated probe will read accurate pH, which is defined by the concentration of H+. But it can't read free CO2 gas that liquid indicator can. So it is the other way around that liquid indicator is less accurate because it reads beyond H+. But if your goal is to use pH to estimate CO2, a pH probe will underestimate CO2 if the proportion of free CO2 gas is high.
My pH probe shows instability and higher pH than my API test kit during injection due to substantial CO2 misting. But pre injection, my pH probe is stable and read identical to my liquid indicator within my color vision resolution ability. But my tank water has higher pH, around 7.5 pre injection, so the color never drops below the chart.
A calibrated probe will read accurate pH, which is defined by the concentration of H+. But it can't read free CO2 gas that liquid indicator can. So it is the other way around that liquid indicator is less accurate because it reads beyond H+. But if your goal is to use pH to estimate CO2, a pH probe will underestimate CO2 if the proportion of free CO2 gas is high.
My pH probe shows instability and higher pH than my API test kit during injection due to substantial CO2 misting. But pre injection, my pH probe is stable and read identical to my liquid indicator within my color vision resolution ability. But my tank water has higher pH, around 7.5 pre injection, so the color never drops below the chart.
