In
re-circulating systems, the nutrient solution must be regularly ‘dumped’
(discarded). This is done to maintain the nutrient’s balance and prevent
the buildup of nuisance and harmful salts (e.g. sodium, chloride),
pathogen, dirt, etc.
In both winter and summer, dump at least every 2 weeks. The dumping
frequency can be less if using low salinity, rain or RO (reverse osmosis)
water.
Salty
water:
More frequent dumping (e.g. every 7 days) may be necessary when using
salty make-up water because nuisance chemicals build up more rapidly to
toxic/ precipitation levels - especially during hot, dry weather.
Method of
dumping:
Poorly designed hardware can make dumping a tedious and messy task. So
consider this at the design stage - or before you buy. Unfortunately, most
system designs are not sympathetic to the hassles of dumping. Consider the
advantages of the following design features:
1.
Install an in-line 2-way valve between the pump and feed outlets to divert
the nutrient flow to waste (Fig 6.1a).
2.
Design a sloping floor into the tank which slopes towards a sump from
which the nutrient is drained (Fig 6.1b). This will help remove the last
few litres containing the bulk of the sediment. Another, simpler, method
can be to tilt the tank towards the outlet.
3.
‘Sump’ pumps are convenient for
draining tanks (Fig 6.1c). They are light, portable and easy to prime,
however, they will typically only drain to a depth of around 1 inch. Hence
a sloping tank floor or built in sump is needed for best results.
Where to dump:
Use the remaining nutritional benefit of the ‘waste’ nutrient by placing
it on your garden or over a large area of grassland etc. Do NOT put down
drains, toilets or in waterways or pour into sand as this can cause
environmental damage e.g. algae bloom.
