SpaBoss No Phos is a naturally formulated hot tub water additive that removes phosphates from spa water. The existence of phosphates in the water can encourage algae growth, as phosphates are nutrients for algae. No-Phos is not an algaecide or algaestat and does not kill algae. Normal sanitizer levels will kill algae and No-Phos helps with the sanitizer efficiency. Regular use of No Phos will help prevent the existence of all types of algae.