PH Buffer 4 is a solution supplied by growth technology. This is a solution with a known, fixed pH and is used for calibrating pH meters, this should be done reguarly to ensure the meter keeps its accuracy.
Just pour out what you need into a measuring cup, and use this to calibrate your pH meter. After calibration you must discard the used solution. Do NOT pour back into the bottle as this may contaminate the bottle and make the solution inaccurate.