If you do not have a phosban reactor (??) this is what they say about the ROWA PHO
Can be used in a canister filter as a separate slow phosphate filter or can be utilized at the end of the main filter system as the final stage after the biological and mechanical filters.
This media can be used in a very fine filter bag or sandwiched between two layers of fine filter floss (on the incoming or outgoing flow).
The amount required will be determined by both the level of phosphate in the water and the level of phosphate in the rocks, gravel and other substrates within the aquarium.
In new or established aquariums where the phosphate levels are high, first measure the level in the water and assume that 2-4 times that amount may be bound up in the substrate and adjust by dividing the recommended aquarium size by 2-4 times.