Well, I am frustrated with this product. At present, I would recommend AGAINST this product. Here's why....
FIRST: I had a devil of a time getting a solid seal on the lid of one of the units. Finally managed to get it leak-free by using a homemade O-ring/gasket and plumber's paste. The other unit I had put silicone around the exterior where the lid fit the body. I suspect that the leak was the primary source of air entering the closed loop and creating a massive venturi effect which turned my DT into a protien skimmer. (bubbles)
SECOND: these things cause water to PULSE through the pipes when the unit is switching. When holding the flexible 1" ID tubing in my hand, I was not able to hold it still, and that was with the SCWDs securely fastened to the wood stand.
THIRD: They are loud. The frequency at which they switch is determined by the rate of water flow. Slower flow means they don't switch as often. Mine was high (2500 to 3000 GPH), so they switched every 30 seconds./ A switch took about 25 seconds to accomplish. So, that is 25 seconds of pulsing water and noise.
The noise from the SCWDs is a rythmical knocking sound about as loud as a relatively quiet, or "polite" clap of the hands. Perhaps slightly quieter than someone knocking with thier knuckles on your front door. Maybe they wouldn't be so loud if the GPH were not so high.
The noise is also the sound of the flexible tubing whacking the side of the DT as the water pulsed thru it.
Alas, my solution to the noise problem will, hopefully, be to mount these babies outside, on the other side of a wall, where I can't hear them.
I'll post again if I have any further info on this product.
