This two-part article describes a simple way to maintain healthy water conditions in show tanks and other short-term holding facilities.

PART ONE: Fish + Water = Chemical Changes

by Dr Peter Burgess

Let's consider the chemical changes that occur when a fish is placed in an unfiltered aquarium.

Initially, the water conditions in the aquarium may be perfect, but within a short period of time the water chemistry will begin to alter as a result of the fish's metabolic activities, such as respiration and excretion. (see diagram).

The overall effect is a deterioration in water quality which, if not addressed, will ultimately harm the fish. Even relatively small chemical changes can affect the fish's deportment and colour, and result in a Show fish being down-pointed.


Ammonia is a waste product of protein digestion. About 70 per cent of the fish's ammonia wastes are excreted via the gills, the remainder being excreted via the kidneys along with the urine. Ammonia is invisible in water.

The build-up of ammonia wastes is a major concern when housing fish in unfiltered systems, especially small volume aquariums such as Show tanks.
As most fish-keepers will know, if ammonia levels are allowed to rise, this can have detrimental effects on the fish. Low levels of ammonia can irritate and damage the fins and gills whereas very high levels are life-threatening.

The rate of ammonia build-up depends on many factors, notably the size of fish relative to the water volume. In small aquariums, where there is minimal dilution effect, ammonia can reach significant levels within a matter of hours.

Ammonia toxicity and pH

The toxicity of ammonia to fish increases with the pH and temperature of the water. Of these two influencing factors, pH has the greatest effect.

For example, any ammonia present in a Show tank containing slightly alkaline water (pH 7.5) will be roughly ten times more toxic than that present in a slightly acid (pH 6.5) tank.

That's bad news if you exhibit species that require alkaline conditions!

Ammonia removal by biological filtration

In the home aquarium we generally install a biological filter to prevent the accumulation of toxic ammonia in the water. Biological filters (or bio-filters for short) function by sustaining vast colonies of bacteria within the filter medium.

It is these friendly “nitrifying” bacteria that convert the fish's ammonia wastes into less toxic nitrite and then to relatively non-toxic nitrate. Of course, when you buy a bio-filter from the shop it won't come pre-seeded with these important bacteria. Instead, the filter has to be switched on in the aquarium and allowed to "mature".


We can define filter maturation as the gradual process by which the filter becomes fully colonised with nitrifying bacteria. This process, with nitrifying bacteria (such as Nitrosomonas and Nitrobacter species), can take 2 weeks or more, being slower at lower water temperatures.

A lengthy maturation period means that we cannot install a new bio-filter in a Show tank and expect it to instantly cope with the fish's ammonia wastes.
By the time the filter was anywhere near mature, the Show would be long over!

The new bio-filter might, however, function “mechanically” (by removing suspended particles from the water); the aquarium water may therefore appear healthy and crystal clear, even though it could be harbouring deadly levels of ammonia.

Filter bacteria need oxygen

One solution to the problem might be to borrow a mature bio-filter from an established aquarium and install this in the Show tank. However this method presents logistic problems.

A major problem lies with the filter bacteria's need for a constant flow of oxygenated water. Filter bacteria, like fish, require oxygen to survive. Once we switch off a biological filter, the cessation of water flow through the filter chamber starves the bacteria of vital oxygen (and food). Within just a couple of hours the bacteria begin to die off.

Hence, we cannot simply unplug a mature bio-filter, transport it long distances to a fish Show and expect it to work with 100 per cent efficiency. Even if we transport the bio-filter in a bucket of aquarium water, many filter bacteria are likely to die as a result of inadequate water movement through the filter medium. Some fish-keepers overcome this by aerating the submersed bio-filter using a low voltage air-pump plugged into the cigarette-lighter socket of a car – but it's a bit of a palaver! Relying on bio-filtration at fish Shows is therefore risky.

So what's the answer? Well, how about using chemical filtration in Show tanks?

Chemical filtration

We have already mentioned two main types of filtration:

· Biological (involving nitrifying bacteria)
· Mechanical (physical removal of solid wastes and other particulate matter).

The third type is chemical filtration.

As its name suggests, this relies on chemical agents that deal with one or more undesirable substances in the water, such as ammonia, nitrite, nitrate, phenols, and heavy metals.

Some of these chemical filters work by
removing undesirable substances from the water,
whereas others form reactions that neutralise
or 'lock-up' the noxious substances, rendering
them harmless to fish
(that's how "Ammo-Lock" got its name).

There are also ion-exchange” (IEX) resins that basically swap noxious chemicals for harmless ones. Unlike bio-filters, these chemical filters work instantly.

Fish-keepers have been using chemical filtration media for decades, notably - activated carbon - that was routinely added to the once-popular air-driven box filters. Of course, we still use activated carbon today.

In recent years, advances in aquarium technology have yielded new and highly efficient chemical filtration media that deal with a wide range of toxic substances and pollutants.

  Many chemical filters are commercially available as
  chemical-impregnated pads or pouches, so they can
  easily be inserted within the chamber of a
  conventional bio-filter.

  Nowadays, even small internal bio-filters
  (such as the Rena Filstar i1) come with an
  optional extension canister that houses a
  chemical filter cartridge.

Chemical filtration media can also be placed in traditional air-driven box and corner filters.

Chemical filtration is therefore perfectly suited for use in temporary housing systems, such as Show tanks, hospital tanks and quarantine units.

In Part Two, top fish exhibitor John Egan evaluates two chemical media for use in his Show tanks and temporary holding tanks.


Want to know more?

For more information about chemical filtration, write to Peter Burgess at:

The Aquarian Advisory Service,
PO Box 5059, Melton Mowbray,
Leicestershire LE14 4ZN.

Or email your enquiry directly to Peter:

Both Peter and John will be at the Festival of Fishkeeping and Water Gardening Weekend, Hayling Island, October 14-16, 2005. Hope to see you there!

For further information about fish and fish keeping, visit us at

Last updated September 2005