Type of filters

Sub gravel filters
Hidden below the sand level, these catch the dirt and concentrate it in one place. The top sand appears clean, so does the water, but the dirt is still there in the tank until and unless you remove the whole filter and siphon off the dirt.


Corner filters
The biggest hoax ever made on the unsuspecting aquarist. The filter is small, neat and cheap; it is so small that it becomes saturated in an hour or two and after that you are just fooling yourself.

Function of the filter

The filter will remove floating particles and some gases, notably carbon dioxide. It will also provide a form of aeration by circulating the water.

It will not remove algae, nor the sediment at the bottom of the tank unless this has been stirred up and is suspended in the water. Thus water suffering from white or green cloudiness is not normally cleaned. Neither will the filter remove parasites that carry fish disease.

Therefore, is it worth the trouble and expense? Frankly, no. Like aeration, it is a useful adjunct but it is not an essential part of the balanced aquarium.

Please note that marine aquaria are not being discussed here, and marine filtration is therefore excluded.

Filtration

Filter is no more than a container for the air lift and the 'three layers'. It can be hung inside or outside the aquarium, depending on its size. The amount of work it can do is governed by its own area and by the rate of the water filtering through it.

The first layer of the filter has to be renewed most frequently, bearing as it does the brunt of the work by removing the larger floating particles. The sides of the filter, if it is being hung outside the tank, should be shielded from excess light, as should all connecting tubes, so as to discourage the formation of clogging algae.

The three layers must, of course, be packed down tightly so that the water has to percolate through and cannot run down quickly. Obviously too the layers will have to be of a reasonable area and of a sufficient thickness.

What is the filter

A filter is a device for removing floating particles of the larger kind from aquarium water and even for absorbing some of the gases therein.

It is usual to connect the air pump to an 'air lift' by means of which the aquarium water can be pumped back into the tank after it has been siphoned from it and passed through the filter.

The filter normally consists of three layers; the first - such as the fine sand, spun glass or cotton wool. Their functions are to remove floating particles. The second layer is the activated carbon which is the core of the apparatus which even removes the gases and some of the organic compounds such as toxic products due to the presence of fish in the water. The third layer is merely a coarse layer of small stones allowing the filtered water to percolate to the bottom of the 'air lift' through which it is pumped back into the aquarium.

Aeration II

What if the aeration stops? There are numerous reasons why this happens, one of them being the failure of the pump. Others may be while we are moving the fish to another tank. For whatever reasons, we should keep an eye for trouble. Fish accustomed to aeration will suffer in still water.

It is better to regard aeration as an auxiliary or a reserve, something that can be turned to for help in case of emergency, such as the sudden arrival of extra fish. Therefore if we have a tank with a small air surface, keep only a few fish. If we have more fish, then get a larger tank.

Putting more fish in an aquarium with small air surface and providing an aeration to them is not a good action. It takes only one fish to catch a disease for all in that cramped aquarium to succumb to it. The cure is to have a larger aquarium, with larger air surface. Providing aeration to overcrowded aquarium is not the answer.

Aeration

It is not true that we can always and at all times double the proper number of fish in a tank just because aeration is provided. The utmost that the aeration can do is to keep the water at full oxygen content and to help eliminate harmful carbon dioxide gas. In fact, it can easily fail to do even that if the water temperature is raised thus automatically lowering the oxygen content. Aeration will also fail to keep the water at full oxygen content too, if the carbon dioxide content is raised by dirt or other matter fouling the tank by the fish present being too numerous, too big or too fast swimming.

Aeration does help but to credit it with doubling the fish capacity of a tank is going too far. If a tank will satisfactorily hold twenty five fish without aeration, then thirty two to thirty seven is the maximum when constant aeration is provided. In this case, thirty to forty per cent increase in the amount of fish is considered reasonable enough when aeration exists.

Why do plants die?

The reasons are:

Their feet are too hot if the tank is above a radiator; a piece of protective asbestos over the radiator should normally suffice.

Too little, or unevenly spaced toplighting, especially if the tank is more than 15 inches deep.

Water too acid.

Not enough fish to fertilize the plants.

Plants were allowed to get too dry after planting.

Not enough room to grow; either thickets too thick or lead weights too tight.

Wrong kind of plants, or more rarely, unsuitable water in the tank for that particular type of plant.