PhosGuard, 20 L / 5.3 gal. Rapidly Removes Phosphate And Silicate From Marine And Freshwater Aquaria Highly Porous For High Capacity And Bead Shaped For Optimum Water Flow Outperforms all competing products Not Recommended For Phosphate Based Buffers In Freshwater Aquaria 250 Milliliters Easily Treats Over 75 Us Gallons