A stable pH is more desirable than a fluctuating one, and while some fish and plants will adapt to something at the limits of their natural range, it is better to select fish and plants already suited to your current water.
pH: A stable pH is also important for the health of your tank and for most tropical fish and plants. Buying fish suited to your local water conditions is advised over using pH-altering chemicals, as these can sometimes be stressful to both plants and fish. Some have limited capacity to remain stable in a given tank (particularly if buffering capacity is low). Additionally, mixing your water to exact pH at every water change can sometimes be tricky, causing your pH to fluctuate. A stable pH is more desirable than a fluctuating one, and while some fish and plants will adapt to something at the limits of their natural range, it is better to select fish and plants already suited to your current water.