Floc

It might seem that Mr. Holl, whose initial sketches are glorious watercolors, was an unlikely candidate for a job that is all about hydrodynamics. But he credits much of his inspiration to repeated meetings with engineers -- as many as 30 at a time -- to discuss topics like "flocculation" (the process by which particles form coagulated masses, or flocs).

This can happen for a few reasons, such as adding too much floc or adding too much algaecide prior to floccing.

This can happen for a few reasons, such as adding too much floc or adding too much algaecide prior to floccing.