For pH calibration buffer solutions, we recommend that users pour the solution in an additional cup or calibration cup if given (and keep the cup closed when not in use). You should replace it with new pH buffer solution in the bottle after approximately 10 times of use. 

For Conductivity buffer solution, we recommend about 5 times of use before replacing new calibration solution. 

Do not put used buffer back in the original bottles. There could be some substances that the sensor acquired to contaminate the solution, therefore if you put it back in, It could ruin the whole solution. And always keep the original calibration solution bottles tightly closed and stored in room temperature.