Bill, I do not have freeze control. The reason I have two diffusers on the Koender windmill is for demo purposes only (Koender Airstone VS Vertex CoActive Airstation)I dont think splitting 1.5 CFM would do a lot.My concern is on the dual diaphram unit with dual diffusers, Superior Windmills clain they maintain equal air to dual diffusers with the 3 CFM Turbo model. I sent them an Email last night and hopefully they will become part of the PondBoss Forum.My limited experience to date on splitting the air supply on the Koender is that as soon as it was turning less tham max and the CFM would drop that the air supply always went the path of least.Seems like the same situation would exsist with 3 CFM as well. Would freeze control (checkvalve perhaps) give additional backpressure to prevent this? Ted
