> It's a slow, steady decline, not a "this goes from fully potent to useless at this moment in time" kind of thing. Yeah maybe you'll give yourself four units and it'll actually be effectively 3.5; that's still better than zero.

The process of flocculation itself is autocatalytic and therefore ~exponential. Though the k factor might be low enough and minor deviations in the exact mechanism that are formulation-dependent might to make it look quasi-linear for quite a long time, followed by a precipitous drop.