Flushing is done to remove
deposits of general dirt, salt precipitates and algae from the root zone,
medium and other system parts.
Pay particular attention to flushing the root
zone and feed circuit. Inspect filters, inlets and feed outlets prior to
replenishing the system with fresh nutrient. These are prone to becoming
blocked with solid material dislodged during the flushing process.
Flushing is done immediately after the
nutrient is discarded. First, do any necessary manual cleaning,
as the removal of any obvious deposit build-up. Then partly fill the
reservoir with fresh water and operate the pump to flush the feed circuit,
medium and root zone. Flushing can be enhanced by spraying with a garden
hose. Discard the waste, then repeat the process until the waste water is
clear and its conductivity is equivalent to that of the make-up water.
Although it is relatively common for
hobbyists to flush only every 7-14 days, some commercial growers consider
it necessary to flush daily. The frequency ultimately depends on factors
such as salinity, temperature, medium, plant variety and general
If flushing can be scheduled to occur when
the nutrient reservoir is empty then the existing system hardware can be
used. Place low alkalinity* water in the reservoir and operate the
nutrient pump until the EC of the run-off water is no higher than ~0.5mS
above that of the water in the reservoir. It can be a benefit to do
additional flushing with a garden hose if the surface of the medium is
If the nutrient reservoir cannot be emptied
to conduct flushing, it will be necessary to have another dedicated
reservoir and pump for flushing (Fig 12.2). This can be connected to the
existing feed circuit at a junction controlled by a 2-way valve. The valve
is simply diverted to the second reservoir whenever flushing occurs.
* Lower the pH of tap water to ~5.0. RO or
rain water will not need adjusting.