You have this sort of lark with wfp, go months with every thing hunky doorey and then a couple of bit will need replacing in a week. However it sounds like you have a problem with your ro set up. The water coming out will always be lower than the water coming in, it sounds like something silly is going on like the waste from the ro going to the resin. That's the only reason I can see to get a higher reading out of the resin than what's coming out of the tap. Simon.