Small amounts of Ca‐H‐humic acid suspension in dialysis bags were immersed in dilute CaCl2 which contained 1.33 × 10‐5M to 6.67 × 10‐5M atratone, atrazine, prometone, or prometryne. Adsorption isotherms were linear. Increases in CaCl2 concentration from 10‐4M to 10‐2M or larger Ca saturation (10 to 100% Ca) of humic acid resulted in less s‐triazine adsorption. Greater adsorption occurred when the amount of Ca‐humate at a specified Ca saturation was increased. An ionexchange treatment of adsorption quantitatively predicted adsorption changes with change in s‐triazine concentration, CaCl2 concentration, and Ca saturation of the humic acids.