A circulation pump is a smaller pump that is designed to run 24/7 in your spa. They are typically plumbed inline with the heater and filtration of your spa. Most circulation pumps also draw less than half as much electric than a non-circulation pump. When plumbed inline with the filter this means you now have 24 hour filtration on your spa, resulting in cleaner, clearer water. For brands that have an inline water care system the circ pump would be plumbed into that system as well providing consistent water care treatment.