Hey, I am having a problem with my tds too, after I have refilled my cartridge, which sounds like the same cartridge at 700ml.
The problem may be that when I emptied my cartiridge of resin, two round spongy parts fell out, should these go above and below the resin or both at the top/bottom of the cartridge.
Any help appreciated, its one of the ones john hewitt sells, pic near the bottom of this page
http://www.johnhewitt.com/ro.htmThanks, Gary