Selenium sol'n; 250 ppm. Increases selenium in recirculating seawater systems. Increases primary productivity. Required by photoautotrophs (including zooxanthellae) for antioxidant activity and critical biochemical processes. 1 drop (0.05 mL) per 24.6 gal. (93.2 L), or 1 mL per 492.2 gal. (1,862.9 L), once daily to maintain NSW value for S=35. 250 ppm selenium, derived from sodium selenite (anhydrous source, USP).