Triton AL99, PO4 remover 5000ml is a high purity, pelletized aluminum-based phosphate remover
Aluminum is very effective at binding phosphate and other types of contaminants in a reef aquarium like silicate, fluoride, and barium. It is suggested that a standard media reactor is used with AL99 with very low flow through the reactor. That allows for long contact time with the media that will bond with certain types of elements that you do not want in your reef tank.
It is important to keep a stable phosphate level in your reef tank. A range of 0.04ppm to 0.08 is acceptable, but stability is the key!