Ted, I have the ALA6GL diffusers on my system. There isn�t a check valve on the airstones. On my blower there is an air filter on the intake side but not on the output. So I probably am getting dust from the vanes in my airstones. I just replaced the graphite vanes last month although the old ones were only wore down about a third after a year of operation. I have a bypass valve on my compressor that allows me to blow off excess air, my one diffuser is bubbling to beat the band but I�m not putting all of the air to it. I had planned to clean/replace the airstones when the water warmed up a little bit. Bill Cody mentioned the membrane type air diffusers, I have a Koi pond that is slightly over 60,000 gallons and I use these. They are built into the domes that cover the four bottom drains. They seem to work very well, do you have a preference? They do seem to be less maintenance, from what I understand if they start to get clogged all I have to do to clean them is to crank up the air and that will expand them enough to unclog them. Thanks for your help, Joe.
