Phosphate sol'n; 50,000 ppm. Increases phosphorus, a critical nutrient for survival of photoautotrophs (incl. zooxanthellae), which often becomes biolimiting (slowing or halting primary productivity and cohort growth) in recirculating systems densely-populated with zooxanthellate cnidarians and bivalves, and/or which employ turf scrubber filtration. P deficiency is associated with bleaching. 1 drop (0.05 mL) per 26.4 gal. (100 L) increases phosphate by 0.025 ppm. 50,000 ppm phosphate, derived from potassium phosphate USP.