Algae: Friend or foe?
“The best form of algae control in hydroponics
will always be prevention by the exclusion of
light hitting the nutrient solution.”
older, more resistant plants, but since hydrogen peroxide is a biocide, rather than an algaecide, there is
always a risk of root damage.
Use of UV light sterilization systems to control algae
in the nutrient solution has mixed results. While UV
treatment will destroy algae spores suspended in,
and floating around, the nutrient solution or source
water as they flow through the UV sterilizer, algae
already growing out in the hydroponic system fixed
to channel and reservoir surfaces will not come into
contact with the UV light treatment chamber and
hence will not be killed. UV doesn’t add any residual
killing effect to the solution—it only destroys algae it
shines on as the nutrient solution flows past the UV
light equipment.
Other studies have found organic algae control methods, such as adding certain grapefruit seed extracts
at the correct dose rate to the nutrient, will kill algae
without harming the plants. This is a method used
in drinking water, ponds and lakes, and it appears to
work well. However, once the algae have been killed,
they will start to decompose and ideally should be
filtered out of the nutrient solution. Algae also tend to
reoccur a certain time period after treatment.
There could be the potential in larger hydroponic
reservoirs to use barley straw rafts as a means of algae
control, which has been proven to work in ponds,
lakes and other waterways for many species of algae.
The aerobic decomposition of barley straw releases
certain chemicals that prevent the growth of algae.
The specific decomposition chemicals have not
been identified, but it is suggested these might be
oxidized polyphenolics or even hydrogen peroxide.
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Maximum Yield USA | February 2014
Left: Lightproof covers are the best way of preventing
algae problems.
Right: Sometimes it seems the algae grow faster than
the plants.
This process is rather slow and probably not the most
convenient for small indoor gardens. It also requires
good levels of dissolved oxygen to always be present
to allow only aerobic decomposition of the barley
straw. There are liquid bottled barley straw extracts
on the market that can be used to control algae in
fish tanks and ponds and are worth experimenting
with in hydroponic systems at low dosages. However,
as with any products that rapidly kill algae, if large
amounts of algae growth suddenly die off and begin
decomposing in the nutrient solution, this lowers the
amount of dissolved oxygen present for plant root
uptake. Large amounts of dead algae are best manually removed or filtered out after treatment with
control products to control the biological oxygen
demand in the system.
The best form of algae control in hydroponics will
always be prevention by the exclusion of light hitting
the nutrient solution. Wherever possible, growers
should aim for this rather than relying on quick-fix
chemical controls.
In Conclusion
Small amounts of algae colonizing a hydroponic system
are not a threat to plant growth, however unsightly
they might look. In the future, growers might even find
themselves using different types of algae extract products to boost plant growth and health.