clean team - thats the 720GPD system.
720GPD = 2721 ltrs (US gallons)
However this is rated at 80psi, inlet temperature 20c etc - best possible conditions. It should be filling your tank quicker than what it is doing so it most likely needs to be backflushed, the easiest way to do this is to use the backflush kit but failing that you can take some 6mm John Guest pipe, push it into your microbore and turn the pump on to flush the system out. You need to close off the product pipe and the inlet in order to force all the pure water through the waste line.
If you need pics let me know.
I'm protectacoting a couple of vans here - high as a kite.