Flushing
is
done to remove the buildup of unwanted/ harmful salts (e.g. sodium,
chloride), root exudates, algae, pathogen (etc) from the root zone, medium
and other system parts.
Pay
particular attention to flushing of the root zone and feed circuit.
Further, inspect filters, inlets, outlets (etc) prior to replenishing
system with fresh nutrient because they are prone to becoming blocked with
solid material dislodged during the flushing process.
Re-circulating systems:
Flushing is done immediately following each dump cycle. First, do any
necessary manual cleaning (i.e. remove any obvious buildup etc). Partly
fill the reservoir with fresh water then operate the pump with the aim of
flushing the feed circuit and root zone/ medium. Flushing can be enhanced
by spraying with a garden hose. Discard waste, then repeat process until
waste water is clear and conductivity is close to that of the make-up
water.
Run-to-waste systems:
Although it is relatively common for many hobbyists to flush only every
7-14 days, some commercial growers consider it necessary to flush daily.
The frequency ultimately depends on salinity, temperature, medium, plant
variety etc.
Flushing
methods:
a)
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. If the surface of the medium is
readily accessible it can be beneficial to do additional flushing with a
garden hose.
* Lower the pH of tap water to ~5.0. RO or rain water will not need
adjusting.
b)
If the nutrient reservoir cannot be emptied
to conduct flushing, it will be necessary to have a dedicated reservoir
and pump for flushing (Fig 6.3). This can be connected to the existing
feed circuit at a junction controlled by a 3-way valve. This valve is
simply diverted to this reservoir whenever flushing occurs.
