Being female, i leave all my van requirements to my hubby. But i would like to learn more about it. Attached is a photo of my ionoc system. All i know is that when the bottom filter is not blue anymore, i have to change it. At a cost of over £100. How often should all the other filters need changing? Can i buy them cheaper else where other than thro ionic? I also have salt for back wash which cost me about £9 for 25k bag. Last about a month, How much do you pay for salt? My tdi is 0.01 so im happy with that at the moment. Thanks in advance for any info and advice.