I've got a 1 year old Carette with the alpha filter and 13 hrs of run time on it. Does the filter element need to be changed at regular intervals or only when it shows signs of becoming "wet"? I've never opened the filter. I plan to do so but not sure what to look for (color change?). Anyone have any experience here? I'm sure Joe would tell me to get and install a fresh element just to be safe but I'd like to know what you think. Uj