Im running a RO/DI unit and really dont want to encounter any of these problems. Right now, Im running about 254 going in and 1 coming out. Sometimes it's hard to determine when to change the filters , without knowing how many gallons of water have been thru it. Are the monitors that you can get at BRS a good investment in monitoring the volume of water that passes through each canister and alerting you when you should change it or is it just cheaper watching the signs of your TDS output and changing stuff when you see the numbers shoot up....but then again, wouldnt that be a little too late. Anyone running one of these monitors?