ive been a merlin user for over 3 years - top bit of kit - still on same membrains , only change the filters when the flow slows right down
merlin is easy to mod to stop to much waste flow -- i run 5mtrs of 5mm tube after the merlin waste pipe , gives back pressure , mine runs 1-2 waste like this - and before anyone says it can damage - its been like this for 3 years ..... runs A1
another tip - dont bother sticking a di on to the end of a merlin - or come to that , onto a tap to fill up a tank - the flow rates are to high to get any ,long life from your resin .
stick a di after pump , but before hose reel - resin will last so much longer as you pumping water through slower giving the resing more time to do its thing.
the resin seller's wont tell you that - they want you to spend £80 every month lol
i must only use a bag a year ...