Two separate procedures are required to
ensure hardware is clean prior to replanting.
"Disease
preventative":
At the end
of each crop, it is necessary to sterilize the entire hydroponic system to
help prevent disease problems in the next crop.
The
following guide will help remove organic buildup e.g. pathogen, algae,
slimes, dead/decaying plant matter (Fig 11.4):
1.
Remove all plants and media then do as much manual cleaning as possible.
External cleanliness is as important as internal.
2.
Partly fill system with water. Lower the water’s pH to below 5, then, with
subdued light conditions, add household chlorine bleach** (50g/L chlorine)
at ~5ml per litre (4 tsp per Gal).
3.
Mix
well then, soak system for 24 – 72 hours. (Note that chlorine bleach will
not dissolve algae or general solid material. Only wet brushing will
remove those contaminants). Suitable treatment over that time includes:
- For
re-circulating system, run the pump for at least 15 minute cycles every
hour.
- For
run-to-waste systems, run the pump for a short burst once every hour.
4.
Afterwards, discard this solution then flush whole system several times
with small volumes of fresh water to remove all traces of chlorine,
dislodged material, etc.
5.
Where fine drippers, sprayers (etc) are used, it may be necessary to
individually dismantle and clean each unit.
Precipitate removal:
Over the
long-term, it is sometimes useful to conduct an acid** flush to help
remove precipitates (white precipitates of calcium sulfate and phosphate –
see Fig 11.4b)
that cannot be dissolved with plain water or wet brushing.
1.
Firstly, treat system as detailed for “disease prevention” above.
2. To
tank, add water and enough hydrochloric acid to achieve pH 2. i.e. if
using rain or RO water dilute 30% (i.e. normal commercial strength) by
around one thousand fold i.e. 1ml per litre (3/4 tsp per Gal).
3.
Soak system for 24 – 72 hours. Suitable methods might include:
- For
re-circulating system, run the pump for at least 15 minute cycles every
hour.
- For
run-to-waste systems, run the pump for a short burst once every hour and
collect the discharge.
4.
Afterwards, neutralize solution up to pH 5 – 6 with soda ash before
discarding.
5.
Flush whole system several times with fresh water to remove all traces of
acid, dislodged material, etc.
6.
Where fine drippers, sprayers (etc) are used, it may be necessary to
individually dismantle and clean each unit.
** Ensure
to follow necessary safety precautions and contact no metal parts.
