In Aquaponic systems that drop below 7.0 pH, oyster shells can automatically buffer the pH back upward. As water becomes acidic, it will erode or eat at the oyster shells releasing calcium and other elements into the system that will slowly correct the pH. We suggest keeping some in your system at all times as an automatic control. Includes 2 cups of shells, 1, 3″ net pot and root cloth. Place the netting in the net pot, then pour in shells. Bury under the flowing water in the pebble bed(s).