Medela Pump Membranes

res932

I use the Medela PIS. Lately I have noticed my suppl my hasn't been as good. I had been getting 40 ounces in 4 pumps or 30 in three pumps (this is daily), but now it has dropped down to about 25 ounces daily. I had read that pump membranes that need changed can be the cause of poor production. How often do these membranes need to be changed? Mine are about 5 weeks old and I exclusively pump, so I do about 3 to 4 pumping sessions a day. How do you know when the membranes need changed and how often should they be changed? Thanks!