hi richard, sorry mate i dont anything about a new filter. but i can defo control my wast and product ratio whith the above ive suggested.
infact when i first got this ro (650 gpd) i did not have a flush valve tap fitted on it so all i used was a plastic ez lok tap style connection from the waste out port and adjusted it manually to get a ratio i wnated.
i found more waste = less product (obviously) but a lower tds.... less waste to product ratio (which is harder on the ro membranes btw) = higher tds, so more resin will be used. hope this helps mate? george