You can find tomes
written on this subject, and with good reason.
However, the reason
there are tomes about it is not that it is horribly complicated, it's just that
there are so many ways of doing it.
Mechanical | Chemical | Biological | Bacteria |UG | Internal | Hang on | External | Fluidised | Trickle
Good fishkeeping is
about good filtration.
It keeps the fish
alive!
Filters do one or
more of three things to the water that your fish live, breathe and excrete in.
1. They
clean it mechanically
by straining the water through different grades of 'sieve'
2. They
clean it chemically
by changing water conditions through reaction, absorption and adsorption.
3. They
clean it biologically
as various bacteria process the organic waste products of life
1,
mechanical
is fairly obvious. You take dirty water, some
means of moving it, e.g. electric pump, air operated lift, and something to
trap dirt i.e. a sieve. The finer the sieve, the smaller the particles you can
remove from the water, the more particles you remove the cleaner the water.
Common sieves
include sponges in various grades, gravel and nylon floss.
As the filter picks
up more dirt it begins to block up and you wash it or replace it!
(If only life were
that simple....read on)
2,
chemical filtration
gets a bit more involved. Some chemicals can
be used to the aquarist's advantage. I'll only discuss a few of them.
CARBON is perhaps
the most commonly used chemical filter in the hobby. It aDsorbs almost
everything, dyes, chlorine, copper, the list goes on and on. Adsorption means
attracting things to the surface. This property of adsorption is not endless
however and carbon has only a limited surface area. Once it is 'full' it not
only won't adsorb any more, it can dump what it already has. Carbon therefore
needs to be changed on a regular basis. It also adsorbs almost every kind of
medication or water treatment you might want to add to your aquarium, so plant
food for example becomes an expensive way of using up your carbon and starving
your plants.
It is very useful,
just don't expect miracles.
ZEOLITE is another
chemical product that absorbs ammonia. This waste product of life is poisonous
to nearly everything so it is a great idea to get rid of it. Like carbon,
zeolite has its disadvantages. It too can only take so much. It too can dump
what it has collected and zeolite only works in fresh water. Salt water
actually causes it to dump and so is used to re-charge the stuff.
Water conditioning
is another function of chemical filtration. If, like me, you live in a soft,
acid water area and want to keep fish from hard, alkaline waters you can filter
the water through something like dolomite chips to correct the situation.
Conversely you can filter hard water through peat to soften it. This is often
better done before the water goes in the tank as you should be trying to
achieve stable, not ever-changing conditions for your fish. Once the water is
treated though, chemical filters like these can be used to keep it the way you
want it.
3
BIOLOGICAL FILTRATION,
deserves to be capitalised. It is the most
important filtration of all. Fish can survive in a fog. Many of them come from
muddy pools or streams. Given a chance, most of them can adapt to changes in
water conditions. What none of them can do is survive poisoning by biological
waste products.
All the waste
products in a tank, dead and decaying plants or fish, excreta and un-eaten food
produce AMMONIA. This is deadly stuff. You could spend all your time replacing
water to constantly dilute this poison but that wouldn't give you or your fish
much peace.
Luckily we have some
help from our microbial friends.
Nitrosomas bacteria,
far from being poisoned by ammonia, feed on the stuff, producing as waste nitrI
tes. These are still pretty nasty but they feed the Nitrobacter
bacteria that in turn produce nitrAtes. While still not brilliant, these
are a lot less poisonous than their predecessors and many fish will survive
their gradual increase in the aquarium.
Latest research
suggests that while these bacteria perform these functions in soil, they may
not be the same ones that work in water
The
bacteria that provide these services have simple
needs; somewhere to stay, a supply of food and a supply of oxygen. Think of the
work they save you! No need for 24hr. a day water changing! A simple home and
some food aren't too much to ask.
Where they stay is
very simple. It's on any surface they can get a hold on; gravel, sponges,
filter floss, carbon, resins, in fact everything you already have in your
filter. Here's the catch though. I've suggested that you wash or replace
everything in your filter on a regular basis when it gets clogged. Bacteria
don't like chlorine (it is put in the water to kill them after all) and
chucking them out doesn't seem to be too bright a notion. Solution; use tank
water to clean your mechanical/biological filter and make sure you have enough
re-usable filter material.
The next item is
food. An empty (new) tank has very little food in it so it has very few
bacteria. Their population takes time to grow and they need some food to grow
on. However if you add loads of fish the bacterial population will be
overwhelmed, the ammonia will rocket, all your fish will die and you'll be
another sorry victim of NEW TANK SYNDROME. Give your tank some time to mature;
add one or two hardy fish to provide some food for the bacteria (DON'T feed the
fish, they'll produce quite enough waste thank you) and/or add a starter
culture. You could even feed the tank. A small pinch of fish-food every couple
of days will degrade wonderfully. As the bacteria increase so you increase the
number of fish in the tank. These bacteria are sods to count though. I
find it much easier to check on their level of activity by checking the nitrI
te level. Once it has risen (because the nitrosomas are working well) and then
fallen off again (because the nitrobacter are working) you can add some more
fish. Remember though that any filter can only cope with so much and fish need
their space too. This is not a never-ending story. Once you reach your limit
STOP. Also please remember that the fish you buy are often youngsters.
Youngsters grow and bigger fish produce more waste. Your tank has a limited
capacity no matter how good your filter so leave room for the adult fish to
fill that capacity.
Filters
There is a bewildering
array of filters on the market so I'll try to make some kind of sense out of
them all for you.
Under-gravel
or UG filters are inside the aquarium, on the
base of the tank, under the gravel. They consist of a perforated plastic tray
with an uplift pipe. The gravel sits on this and the water goes down through
the gravel, under the plate and up the uplift tube. The filter bacteria
deoxygenate the water but the return is at the tank's surface so the water
picks up oxygen there.
Internal
filters sit inside the tank. They generally
consist of either a simple sponge or a container of some sort to hold media and
some form of pipe or uplift. The water goes through the sponge or into the box
and through the media before exiting through the uplift. Like the UG filter the
water can be drawn through the uplift either by an air column or by a
power-head. Again the water is deoxygenated going through the filter so the
return should be fairly close to the surface. Some pumps have venturi fittings
that add air bubbles to the returning water.
Hang
on filters do just that. They hang on the back or
side of the aquarium. Water is pumped or syphoned into them and is either
pumped or overflows back into the tank. These filters are generally easy to
maintain as they are accessible without taking the tank to bits or getting too
wet. Water picks up oxygen as it flows back into the tank.
External
canister filters are very flexible. They consist
of a sealed container topped by a pump. Water syphons into the container and
passes through baskets containing a range of media before being pumped back
into the tank. Older canister filters could be tricky. Getting the syphon to
start involved a lot of sucking on pipe ends and disconnecting the filter for
maintenance could lead to large amounts of water on the floor if the syphon
hadn't been stopped. Newer versions have built in priming pumps and fittings
which automatically switch off the water flow when the pipes are uncoupled.
Their bonus points are a fairly large volume of media and the ability to use
several different media in one filter. The return water can be fed back through
a spray bar that agitates the water surface for oxygen.
Fluidised
bed filters consist of a sealed unit through which
clean water is pumped. The biological media is normally sand. This is kept in
suspension by the water flow. This prevents clogging or packing of the media
and exposes the maximum surface area to the water. The flow rate is adjusted to
prevent the media being washed through into the tank. The turbulence in the
filter also cleans the media surface, getting rid of dead bacteria. The return
flow should be at or near the surface.
Trickle
filters are very efficient and have often been
used in marine aquaria. Water overflows or is pumped from the tank. It passes
through floss as a mechanical filter before trickling over a column of media (
often plastic ) into a sump. The column of media is open to the air so there is
a lot of oxygen available to the bacteria in the filter. Other equipment, like
heaters and protein skimmers can be housed in the sump along with a pump that
returns the water to the tank. The water is continually oxygenated as it passes
through the filter.
In planted aquaria
too much oxygen and the loss of carbon dioxide can inhibit plant growth. In
these aquaria the filter return should be 3-4" below the water surface.
Filter
Types
Whatever kind of
filter you have, remember that the health of your filter will affect the health
of your fish. Filters need regular cleaning to maintain a good flow of water
through the media but the bacteria need to be protected while this is done. For
UG filters you can clean the gravel either by raking through it then syphoning
out the mulm from the surface or by using a gravel cleaner when you change the
water in the tank. For other filters the biological media needs to be rinsed in
TANK water to clean it.