Closed loop systems, typically hot and cold water recirculating systems, are often ignored when it comes to water treatment programs. Not only should closed loops be chemically treated to control corrosion and microbiological growth, they should also include a side-stream filter to remove suspended solids. 

Even though closed loop systems are theoretically “closed,” suspended solids can still be introduced as a result of corrosion, new construction, new additions to older systems, leaks, and poor commissioning practices. Turbidity or discoloration can be one sign of suspended solids.