Thanks Ian, Ive ordered some calibration fluid to adjust the accuracy.
You are spot on about unchecked meters, the one I used had been on my 450gpd for two years so who knows if the readings from that were accurate!!! I also have two hand held meters to check water tds at various times, I will re-calibrate all my meters.
Back to my new 4040, now a lot happier with it, last night filled 700 litres into my tank in a mater of around 3 hours, my old 450gpd ro used to be running almost 24/7 to keep up with my water demands.
Thanks everyone for your advice, it is appreciated.
Steve