FCS no disrespect but what's the point in having X2 Vessels half full ? You may as well just have the X1 full which should be about 3 to 4 inches below the top !!!
The point is that when I was using one vessel and the TDS crept up to 10+ it was STILL bringing it down from 20+ to 10. So it still had some life left in it.
As I had a spare vessel I thought I'd just add another vessel in line after the first one to polish off the final 10 TDS.
When the first vessel fails to bring any TDS off the RO output, I throw the resin away, wait for the remaining resin to start building up and repeat the process.
(just seemed a bit of a waste throwing away resin that was still working but not quite good enough, it elongates the life of the new resin)
Does that make sense?