Yes a bit confused over this. Its a 4020, with axeon membranes, and the usual pre filters (sediment and fibredine one for the chlorine etc) I used to get roughly a liter in 25 seconds, which has slowly gone up to nearly 40 seconds. The thing is, its still getting the tds down plenty low enough. I thought if its deteriorating then the tds would be higher as well as producing slower? two tds meters say the ro is getting it to 8 ( from 330 odd, our water was over 500 so thats another mystery) So really what im asking is, can my membrane be on its way out, yet still be getting the tds low as usual? just seems strange. Ive only produced about 30,000 litres of pure from the membrane by the way, but guessed because of our terrible water it wouldnt last well. ( always changed the pre-filters at correct time too) Bit tricky, but any advise, as always greatly appreciated ?