J u n e 2 017 47 UV & Ozone
Ozone
Ozone is O3 – three oxy-
gen atoms linked together
as a molecule. The ozone
molecule is highly unstable
and reactive; it doesn’t really
like to exist as O3, and one
of the oxygen atoms breaks
away, making it available for
oxidisation. There are several
benefits to using ozone in
the aquarium:
- Firstly, it helps to create clear
water, by oxidising yellowing
compounds, breaking them
apart for removal by skimming
or for degradation by bacteria.
This is by far the most popular
use for ozone in the aquarium. - Ozone can also directly oxidise
ammonia to nitrite and nitrate,
reducing the load on the filtra-
tion of fish-only systems. - At low doses, ozone can
make skimming more efficient
through a process known as
microflocculation, whereby
dissolved organic molecules
clump together for easier
removal. In fish-only systems
where ozone has started to be
added, we often see a reduc-
tion in the bacterial sludge
layer of the filter. This is because
heterotrophs have less organic
matter to deal with in the filter
thanks to them being more ef-
fectively skimmed out.How is Ozone Made?Ozone is usually produced
in situ by treating air with an
extremely high voltage (the
corona discharge method),
or less commonly by using
ultraviolet light. The efficiency
of a corona discharge ozone
generator (or ozoniser) can be
improved by passing its output
over an air-drying device (in
its simplest form a cartridge
containing silica gel which
must be recharged or replaced
regularly) – corona discharge
units produce less ozone withincreasing humidity, so a drying
device can help to improve
the efficiency. Another good
reason for using an air dryer is
that one of the by-products of
passing ozone through moist
air is nitric acid (HNO3). Nitric
acid is formed from water react-
ing with atmospheric nitrogen,
and we don’t want to introduce
this into the aquarium. In the
absence of an air dryer, fitting
a limewood air diffuser on the
inlet can help in this regard, as
well as filtering out dust and
salt which can otherwise ham-
per the unit’s performance.Dosing ozoneOzone can be extremely dan-
gerous and should never be
added directly to the aquarium
water. Fortunately, you prob-
ably already have a piece of
equipment which is an excel-
lent way to dose it – the protein
skimmer. The skimmer is ideal
because it allows for very ef-
ficient mixing of the ozone inthe water, and removal of any
flocculated organics.
The skimmer and all of the
associated parts (such as airline
tubing and ‘O’ rings) must be
ozone-safe – the gas is so reac-
tive that it can quickly destroy
some types of rubber and plas-
tics. Most skimmers should be
safe, but check before dosing.
In most cases, all that’s needed
is to connect the venturi or
aspirator intake of the skimmer
to the ozoniser. In some cases,
an additional air pump may
be needed to force air through
the air dryer and ozoniser, and
if you’re running an air-driven
skimmer, this will be the ar-
rangement you’ll need.Tip: The use of a non-return
valve placed after the ozone
generator is recommended to
prevent any backflow of the
aquarium’s water into the unit
in the event of a power inter-
ruption.Controlling the dosage is vital
as overdosing can be cata-
strophic; it’s best to size a unit
so it theoretically can’t deliver
too much ozone, or programme
it appropriately. The range of
acceptable dosages for ozone
is 2.5 to 10mg per 100 litres per
hour, but realistically you can
get away with much less than
this to achieve clear water.
The most effective and saf-
est way to control dosing isOzone is extensively used in public aquariums, principally for its ability to create
clear water.
Redox controllers offer the safest way of preventing accidental ozone overdos-
ing.If an air dryer is not available, fitting a wooden airstone on the inlet side of the
ozoniser can help to dry the air and filter out dust and salt.