Aqua Master Calibration Solution pH 7.00 500ml (Case of 8)Description Aqua Master Calibration Solution pH 7. 00: This solution comes in a 500ml size and is traceable to NIST standard. It is important to close immediately after use to maintain accuracy. The solution should be stored between 59 77F for optimal performance. Any used liquid should not be returned to the bottle. Sold as a Case: This product is sold as a case of 8 bottles. It ensures that you have plenty of solution for your calibration needs.