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