I have a kent 24gpd ctf unit I just got the stuff needed to convert to 50gpd tfc, my question is were do you put the flow restrictor on the intake, or waste water line? very little good water whole lot of waste water just wondering was this normal because at this rate it will be 2 days before I have 50gals. One more ? what are the black spots under the sand bed about the size of a dime?