I’ve had Axeon HF5 membranes for years, but something has happened to the quality of them. They used to last 4-5 years, now they last about a year. Annoying.
So, this time I got a spectrum hf4 membrane from window cleaning warehouse. It’s about half the price of the Axeon, and even if it lasts a year I’ll still be better off.
Currently it’s coming out at 2ppm (been using it for a week)