nutrient pumping cycle
 

Greetings from South Africa I am seriously considering starting a garden along the lines of your design. One question, when the nutrient pumping cycle is on I can understand that the excess is returned to the sump via the overflow, but when it is the off cycle how does the system drain back into the sump? Does it simply flow back through the pump, that is that the pump cannot be of a positive diplacement type? Thanks for a very informative site. If possible could you e-mail me at colinho@bf.new.iscorltd.co.za Thanks a stack Coiln Holman

Yes that is correct. Submersible pumps are better for flood and drain systems or when solution reclamation is a must. Positive displacement pumps are used for drip or other systems when a litter excess runoff isn't a problem.
Ron