Are you getting a scale build up in your recirculation system from your manure holding ponds (lagoons)? Is it calcium carbonate or struvite (magnesium-ammonia-phosphate) crystals? In some CAFO sites, they will use anaerobic lagoons to reduce the amount of manure that they need to treat. In a zero oxygen environment the anaerobic bacteria will take the manure which is loaded with nutrients and further digest it to generate methane, hydrogen sulfide, ammonia, phosphate and other mineral salts (calcium and magnesium). When recirculation from lagoon to lagoon, struvite will gradual form and start to block valves, pumps and pipes.