The invention features a system for treating liquid including a liquid treatment device comprising adsorbent media for removing a substance from liquid and a pH adjuster device located upstream of the liquid treatment device relative to a direction of flow of the liquid. The pH adjuster device contains particulate or solid state pH adjuster material capable of releasing H or OH groups into the liquid or consuming H or OH groups from the liquid effective to raise or lower the pH of the liquid while it passes through the media. The pH adjuster may include acidifier or basifier material. Also featured is a method of using the device to remove a substance from liquid by adsorption and/or ion exchange.