Lanthanum Chloride (LaCl3) is a safe and effective chemical used for treatment in aquari-ums, water parks, residential waters as well as in aquatic habitats for the prevention of algae growth. anthanum is a rare earth metal that is very effective at preventing build up of phosphate in water. In the form of Lanthanum Chloride a small dose introduced to phos-phate laden water immediately forms small flocs of LaPO4 pre-cipitate which can then be filtered using a sand filter LaC13 is especially effective in reducing very high phosphate concentrations.