http://www.genhydro.com/genhydro_US/...structions.pdf
^^^^^^^that there is the inst manual for the waterfarms unit and it dont re circulate nuets it uses a gravity system. when the level of nuets in the bottom resv bucket gets low the valve allows a thined out mix of food to be fed into the system and then it uses the same princible as an aquairum to "bubble" nuets to the top feeder ring. to me this is different that the drip feeding that others use and is more common. im not sure but with this system not only do u have to have a PH meter but you have it use it in the resv, the bucket and in the feed lines (more work?). in my setup i just change the food every 5 days. i already know that the water in LA is hard but not hard enough to make the nuet toxic as long as im not lazy about changing it. and this place might not be heaven but the water is well tested and consistant in what it has in it.