Use 50 grams for every 50 gallons saltwater or 100 US gallons freshwater. Leave product in place for 4 days, then test phosphate or silicate concentrations with either the Seachem MultiTest Phosphate Test Kit or the Seachem MultiTest Silicate Test Kit It may be used in a canister filter, media chamber, box filter, or any high flow area of a trickle filter.