Seachem PhosGuard rapidly removes phosphate and silicate from marine and freshwater aquaria. Although Seachem PhosGuard is effective in both fresh and marine water, it will operate better in seawater and the need for it is better defined in seawater. It is not recommended for phosphate buffered freshwater (Seachem PhosGuard would remove the buffer until saturated). Seachem PhosGuard is highly porous and bead-shaped to promote easy water flow through and around it, thereby increasing both its efficiency and capacity.