Biofilter Problem Solving Guide For Pond or
Water Garden Enthusiasts
This web page is structured in the form of a
question and answer as follows QUESTION followed by
good general advice and then a specific comment.
HOW DO I PREVENT MOST BACTERIAL DISEASES IN MY POND?
Excellent biofiltration and feeding high quality
food will generally result in few problems with
In most countries Aeromonas and Pseudomonas bacteria
cause ulcer and dropsy diseases. Once the disease is
established it is very difficult to eradicate and
whole collections of expensive koi can be wiped out.
There is only one method of prevention and this is
by using products that compete in an aggressive way
with these bacteria. Ask Bradshaws for advice here.
KEEP YOUR BIOFILTER WORKING IF YOU HAVE TO
SWITCH OFF YOUR WATERFALL PUMP AT NIGHT TIME.
If you cannot run your waterfall pump at night -
for example it may make too much noise - then
install a second very small pump that just runs
overnight & that will keep water flowing through the
The bacteria in a biofilter die if they are
starved of oxygen for more than 5 hours which occurs
when the pump is switched off overnight. Once dead
the bacteria take between 4 and 6 weeks to become
viable again. By installing a low cost efficient
pump such as a Hozelock Cascade 1000 the filter is
kept alive and the flow of water can be diverted
direct to the pond without making a noise.
WATER REMAINS DIRTY EVEN WHEN A BIOFILTER IS
There are a number of possible reasons for this
but the most important is that the mechanical
section of the filter is not doing a good job. You
need to check if water is able to by-pass the
mechanical section - for example are there gaps
around the sponges or are there holes in the
There are a number of possible reasons for a
filter not working mechanically this. You need to
check if water is able to by-pass the mechanical
section - for example are there gaps around the
sponges or are there holes in the sponges. If the
mechanical section is in perfect condition then
algae could be the cause. Algae is not always green
and it is so small as to be able to pass through
IMPROVE YOU BIOFILTER 50 TIMES
Replace your present filter media of plastic
balls, tubes, and other devices by Alfagrog.
Alfagrog is a very porous inert ceramic filter
medium. It is produced in England especially for
water purification. It is unmatched for
effectiveness and value for money. One litre of
Alfagrog is sufficient for a biofilter handling
1,500 litres of pond water. Each piece of Alfagrog
is full of tiny holes. 1 litre has a surface area of
between 40 and 100 square metres for the bacteria to
grow on depending on particle size. Compare this
with plastic bio media which have a maximum of 1
square metre per litre.
WHY DO I NEED A BIOFILTER?
In a swimming pool the sand filter does the job
of removing solids and particles that remain
suspended in the water. This is filtration namely
the removal of solids from liquids. However the
filter does not purify or clean the water. This job
is done by the use of chlorine based chemicals. In
this way it is safe to swim in the water because all
the harmful bacteria are killed by the chlorine.
Food is eaten by the fish, is partly digested and
partly expressed as a waste product by the fish. The
fish needs to urinate and this passes into the water
also. Toxic chemicals build up. The biofilter
purifies these chemicals. Without the biofilter the
fish would poison themselves to death. The secondary
reason for a biofilter is to remove solids to allow
clear water to be obtained. Its first job however is
to purify the water.
HOW LONG DOES IT TAKE FOR A BIOFILTER TO START
When a new pond is built it will typically take 4
to 6 weeks before the biofilter is working
effectively. Therefore during this period introduce
new fish slowly.
A continuous supply of oxygen is required to
enable the bacteria in the filter to live. This is
why a pump must work 24 hours per day since the
water is the source of oxygen for the bacteria and
without the oxygen the bacteria die quickly and
certainly within 8 hours. Once dead the colony takes
4 to 6 weeks to build up again
PREVENT YOUR WATER FROM GOING GREEN
Install an Ultra Violet Clarifier of correct
wattage for your size of pond. 8 watts is normally
big enough for a pond up to 5,000 litres.
Water goes green because the algae which feeds on
nutrients in the water provide it with food. This
together with bright sunlight can happen very
suddenly. Because algae is very small (4 microns) it
is almost impossible for a normal filter to remove
it. If water containing algae is passed through an
Ultra Violet clarifier the algae are killed and they
clump together making it possible for them to be
taken out in a good biofilter.
DOES AN UV CLARIFIER UNIT NEED ANY MAINTENANCE?
Ultra violet clarifiers (UV for short) have been
one of the best inventions ever for the pond keeper
but surprisingly only a very small percentage of
pond keepers know of their existence.
One very important maintenance point has to be
made. The UV lamp inside the quartz tube has to be
replaced after about 8,000 hours use which is every
year in practice. This is a must because the lamp is
useless after this period. The best time to install
a new lamp is in Spring. So if your pond starts to
go green even if the 1 year is not up it is probably
time to replace the lamp in your UV unit