I'm here I've just been staying in the background. A lot of people give good advise and many have different whys they run their systems. You have large amounts of sediment in the Twin Cities area, iron being number one. Changing your sediment filter every three or four months is just good management and they only run $3. If your municipal water filtration system is using chlorine as disinfectant it all depends on how much water you make and the quality of your carbon filters as to how often they need changing. Chloramine is found in only 20 of 950 Minnesota municipal water systems and Cottage Grove is not one. It is a good idea to run a TDS meter for you DI and a dual DI system is better when your DI is exhausting fast. You can get a color change and low TDS reading with a single housing without all your resin being exhausted. David really has the system down and you can't go wrong on his advise for RO/DI.rihanssu said:thanks alot david! i'll get ahold of fahz!