ok so just to clarify, i could have the tank full of tap water, and run the water from the tank through the vessels upto the window whilst maintaining 35-40 flow on the digital varistream (out of 100)? no more questions today i promise
Yes, exactly!

You could run the pump at 100 & it would still purify at 000ppm & still be a slower flow through the vessels than mains pressure.
Start off with one vessel until it begins to read 001/002/003 etc, THEN, add the second vessel full of fresh resin after the original vessel. So, you'll now have, in this order-
Tank>pump>vessel 1 (older resin)>vessel 2 (new resin)>hose reel>pole.
When the newer vessel (number 2 above) starts to read 001/002/003ppm, move it to where vessel 1 is. Remove vessel one (oldest resin) & fill it with fresh resin, then put it back where vessel 2 was before. You've just got rid of the oldest resin (original vessel one) that you would have had to throw away ages ago if you were to use just one vessel.
It works in a cycle now, swapping the vessels back & forth, so you're always pre-filtering your newest resin with your old (which is still actually purifying water)
NOW, with my tap water being 90ppm, the old resin never gets this high before the newest needs changing anyway BUT, with tap water at 30ppm you'll have to keep an eye on it, as you don't want the tds in it going higher than the water that it's purifying.
It's very simple in practice & an obvious solution once you get your head around it.
