Aquatic Life Reverse Osmosis Pressure Gauge w/Press-Fit Tee Connectors 1-150 PSI. Sufficient PSI is essential for the correct operation of a reverse osmosis unit. Low water pressure is a leading cause of poor RO system performance. A pressure gauge assures that proper pressure is being supplied. It will also make pressure drops readily visible which can tell you that sediment and carbon blocks need to be changed. Pressure gauge comes assembled with 1/4" quick connect fittings for quick easy in-line installation. This item is designed for use with most aquarium RO systems. Item 9000903.