My guess would be that your first set of filters may have been broke or not of good quality. I hear this a lot from people that have RO systems, at first I was guilty as well. In perspective let's think that most systems are 75gpd. That really is a trickle. The math to support. 60 minutes in an hour x 24 hours in a day= 1,440 minutes in a day / 75gpd = 19.2 What that means is that a typical system takes 20 minutes to produce 1 clean gallon of water. That is just a trickle. It would take almost an hour and half to fill a 5g container. If your membrane was torn water may have been blowing right on by and into the resin chamber. There is nothing in that chamber to cause it to slow down. Your resins could still absorb the excess TDS until spent, thus giving a true reading of 0-4PPM of TDS until exhausted.