I recently had the opportunity to see the conversion of a cooling tower from standard chemical water treatment to a new "Non Chemical Water Treatment Device". In this instance the unit installed was called a Fluidtron. These pictures were taken at about 90 days into the non chemical water treatment program. While the algae build up is troubling it is a minor problem compared to the aggressive corrosion cells that developed. The customer ended up re-coating the tower basin with an epoxy and installed brominators to add Bromine to control the algae.
A quick search of vendors selling this product uncovered some marketing literature. One brochure stated that the unit "eliminates the need for chemical treatment" and listed the benefit of "extended life of equipment" because "reduced corrosion rates extend equipment life". Certainly one case study does not reveal enough data to draw a conclusion, however, in my opinion the results achieved here border on negligence.
I am not implying that all non chemical water treatment devices do not work but the end user should to do their homework before making an investment in a "new" system that is designed to protect the heart of a buildings HVAC system.