A plant can run a textbook-perfect biological phosphorus removal process in its aeration basins and still watch phosphorus quietly reappear as rock-hard scale clogging its digester piping and centrifuge lines — because phosphorus removed biologically doesn't disappear, it moves, and if an operator doesn't understand where it moves to, it can come back to bite the plant in a completely different part of the facility. This is Part II of the Class A Secondary Clarification & Nutrient Removal series, covering the operational trade-offs between biological and chemical phosphorus removal, the struvite scaling problem that biological phosphorus removal can create downstream, and what is currently known — and what remains unverified this session and must be confirmed directly with CDPHE — about Colorado's Regulation 85 nutrient management framework. Part I of this series covers nitrification/den