I have a TDS of 240 in tap water. On one DI vessel filled about 250 litres then TDS went from 0 to 5. Seems to have stayed on that, until what TDS can u clean windows at? WHen it gets to that will switch DI vessels around. Also, when filling DI vessels with resin, I heard on 11 litre ones, fill with 8-10 litres of resin. Is it worth measuring the litres of resin to get the right amount in?