Ebb & Flow System
Ebb & flow systems are similar to deep flow, except that root oxygenation is achieved differently. Where deep flow boosts the oxygen content of the nutrient solution itself, ebb & flow allows intervals in which the plant roots are exposed to air.
During the "flow" period, nutrient is pumped to the grow chamber for a pre-determined interval. The drain pipe height is adjusted to keep plant roots submerged during this period.
When the timer shuts off the pump, the "ebb" period begins, and the nutrient drains back to the reservoir through the pump. Roots are exposed to increased oxygen during this period.
Ebb & flow systems must be more closely monitored, however, as timer malfunction or pump failure can lead to plant loss if the roots remain exposed too long and dry out.