If we can clean with 15-30, why do we bother with di resin? We could save a fortune not buying any
Because you can't be 100% sure what the 15-30 is made up of, so technically to be safe, staying under ~12ppm should be fine. Staying at 000 is just the ideal standard. In my opinion, you should never go DI only to begin with, it's a waste of money and time. Even if you have 30 coming out of the tap, I'd still use a membrane. It's much more economical. Especially at that tds level your membrane and prefilters will last a very very long time.
good post above, as he has stated 000ppm is ideal especially on
first cleans the water is a more aggressive cleaner the less mineral
content it has. i regularly use water up to 10ppm on maintenance
cleans with no problems, anything above that though i have noticed
spotting on properties but thats dependent on the windows and
where the properties are situated e.g. busy roads.
so personally i dont go above 10ppm to be safe