Abstract: Recirculating tube cleaners pass through inside diameters in a bank of heat exchanger tubes. Variable density tube cleaners are provided which are pressurized to compress and have a substantially neutral buoyancy upon entry from an inlet manifold to the inside diameter of the tubes. Upon exiting from a heat exchanger outlet manifold, the tube cleaners return to either positive or negative buoyancy depending upon the embodiment. Skimmer means intercept tube cleaners having positive buoyancy from the upper portion of flow and direct them to a recirculation system. Open cell elastomer tube cleaners having negative buoyancy may be intercepted at the bottom of the flow and then partially dewatered for adjustment toward neutral buoyancy. As contrasted to prior art embodiments in which the entire outlet flow must be screened, here only a small percentage, for example one percent of the outlet flow, need be intercepted.