Saltwater Aquarium Filters

Before we go deeper with Saltwater Aquarium Filters, there is one basic question: Why filter the water? Once an aquarium is put into operation, the characteristics of the water change fairly rapidly. These modifications are a result of the biological activity of living beings plants, fish, and invertebrates, as well as various chemical reactions that occur in the water and sediment. In this way the water gradually becomes loaded with suspended matter - animal excrement, vegetable debris, surplus food, sometimes even dead bodies and suspended solids produced by the activity of the occupants.

Of these, the most significant are the nitrogenous products released by animals' liquid excretion. These substances are very toxic, and so their accumulation is a cause for concern. The suspended matter remains in open water, or ends up as sediment. In either case, it is visible. The suspended solids. on the other hand, are not visible, and therein lies the danger. It is however, possible to observe a slow modification of the water color; in the long term, it takes on a yellowish color. This alteration can be detected very early on by immersing a white object.

Filtration therefore aims to trap the suspended matter, in order to attain clear water that is more receptive to the penetration of light and avoid any risk of intoxicating the residents of the tank. As we have already pointed out, filtration also contributes to good oxygenation. You must not, however, neglect to remove the biggest scraps yourself.

Principle of Filtration
Several filters function by retaining suspended matter: this is mechanical filtration. The filtering media gradually become clogged and must be cleaned or changed. In order to transform nitrogenous sub-stances and encourage the nitrogen cycle, oxygen and good bacteria are required: this is biological or bacterial filtration. The biological filter therefore comprises a support that will be colonized by bacteria, with circulation of water to provide oxygen. The medium in mechanical filtration serves the same function as a biological filter once it has been colonized by bacteria.

The Various Filtration Systems
• The Under-Gravel Filter
The water travels from top to bottom through the sand and is taken back in under a platform that is slightly raised from the bottom of the tank. The water is then pushed out into the aquarium by means of an air-lift fed by an air pump.

Here, it is the sand which acts as the filtering medium, via a double action: first mechanical, as it retains the particles that are in suspension, and secondly biological, as the nitrogen cycle is created by the bacteria and the oxygen supplied by the circulation of the water. The size of the grains of sand is therefore important, as it must allow both the water to pass through and the particles to be retained. This is why you should avoid sand that is too fine and, at the other extreme, sediment that is too thick.

The under-gravel filter used to be extremely popular, but these days it has given way to other techniques. However, it can be used in small temporary tanks or in a community tank, but with a slow and continuous flow, as a complement to another filtration system.

The under-gravel filter Advantages :
- Inexpensive;
- easy to install;
- little or no maintenance;
- easy to camouflage;
- fed by an air pump (often the same as the one used by a diffuser);
- the water clears quickly

The under-gravel filter Disadvantages :
- It must be put in before the bed, when the aquarium is being built;
- it can only, therefore, be removed by taking out all the decor, vegetation, and bed
(which means reconstructing the aquarium);
- the sand builds up rapidly, according to its density, and must be cleaned
(taking us back to the point above);
- draining the bed is not beneficial to most plants with roots;
- the base of the air-lift may become blocked if it is narrow (under 1 cm);
it can be cleared by blowing down it, or by using a long thin rod;
- when the filter is inactive for a while, there is a risk of deoxygenating the bed, which
can cause the development of toxic products.

• The Air-Lift

This ingenious system allows water to be raised to a certain height and also helps to stir, and therefore oxygenate it. As a rough guide, an air-lift with a diameter of 3 cm, fed by an air pump, has a flow of several hundred liters per hour, with a water depth of 40 cm.

The air-lift makes it possible to use an under-gravel filter or a drip filter, or send water from a box filter into the aquarium. In order to reduce the noise of the bubbles and enhance the circulation of the water, its top section can be bent to be flush with the surface.

This under- gravel filter is used with a thick sediment that serves as a filtering medium

• Small Internal Filters Fed by Air
These also work with an air pump, but a small filtering medium, often made up of foam, replaces the sand. They are only effective in small aquariums with a capacity of 50 liters or less.

You can make this type of filter at home. Take a PVC receptacle that is easy to cut, ideally a bottle with a capacity of 1.5-2 liters. The use of foam tends to make the apparatus float to the surface, so you must insert a ballast to weigh it down. The upper part of the foam can be covered by coarse, heavy material, such as gravel or sand, serving not only as ballast but also as a pre-filtration element.

A Quick Way to Make a Small Internal Filter

• Small Internal Filters With an Electric Motor
The motor makes it possible to draw up the water through a thick grid that blocks the passage of the larger pieces of debris. The water is then guided towards a filtering medium, such as foam or Perlon, before being expelled into the aquarium.

This system works well but is insufficient for an aquarium with a volume of over 100 liters, although there are models available that can be adjusted according to the volume of water being treated and that will prove effective.

Small submerged filters with an electric motor

• External Filters
The water siphoned into the aquarium passes into a filtration bay containing several filtering media and is sent back into the tank by means of an electric pump. There is a variety of models available, depending on the power of the pump and the volume of the filtration bay. It is even possible to find filters for garden ponds. These filters are highly efficient; their main disadvantage lies in the amount of space taken up by the equipment, with the pump and filtration bay outside the aquarium, and the pipes for sucking in and expelling the water inside.

External filters with an electric motor

These are suitable for large aquariums - some have a flow of 1 mV hour - and contain materials with various particle sizes in the filtration compartment. They must be placed at the bottom of the tank to avoid any possible draining.
These filters are more expensive than those already described, but, though they are mechanically very efficient, they are not effective in biological terms. The use of particles of different sizes prevents the apparatus from getting blocked up too quickly. It is easier to clean if you have the foresight to install faucets on the pipes.

• Box Filters
These are sometimes built into some aquariums on the market, but they can also be added afterwards. In the latter case, they must be hidden by exterior fittings. The use of this type of filter is becoming more widespread, as it is easy to put into operation and maintain. In a large aquarium, however, its mechanism -the retention of particles - can prove insufficient, and so a complementary external filter must also be used.

The box filter is normally placed on one of the sides of the aquarium. Wherever it is put, it is vital that the volume of the filter is equal to at least 10% of the volume of the aquarium. In the diagrams above, the aquarium is seen from above, with the front at the bottom of the drawing; the foam is represented by hatching. The decor can be artificial.

1. Entrance for water through a hole in the glass, protected by a grid. A siphon with a strainer on the end (la) can also be used. The grid or strainer prevents fish passing through, apart from the smallest fry, which can sometimes be recovered in the box (2). Both must be maintained regularly, as various bits of debris, particularly vegetal matter, build up there, slowing down or even preventing the circulation of the water.
2. Box. This can contain a pre-filtration material, such as Perlon. In saltwater, it is an ideal replacement for the protein skimmer.
3. Filtration foam. This retains fine particles and is the medium for the biological filtration. It is easier to maintain if it is divided into two approximately equal parts.

4. Sump for keeping water before it is sent back into the aquarium by a pump or air-lift. This part of the box filter can receive heating and aeration. There is a variation on this system: the double box filter.

• Wet-Dry Filters
Here, the filtering media are not totally submerged in the water, but are sprinkled by it. This means that they are in permanent contact with the air, encouraging good oxygenation of the water and effective functioning of the nitrogen cycle. This technique is particularly popular among experienced fish keepers.

There are two systems: the gutter filter, which has long been in use, and is easy to set up, and the more recent wet-dry filter, placed under the aquarium, which requires more space. In both of these cases, coarse pre-filtration media are desirable.

- Gutter filter: the water is pushed up from the aquarium by an electric pump or an air-lift to a horizontal gutter equipped with filtration material. The water then passes along the gutter and falls as 'rain' into the tank, thereby enhancing the oxygenation. Chicanes can increase the time taken by the water's journey and, therefore, its oxygenation.

- Wet-dry filter under the aquarium: this is considered the ultimate filtration system by some aquarists. The main problem in setting it up lies in the incorporation of an outlet for excess water in a side wall or the back of the tank. The water descends into another tank and drains through the filtering medium, before being pumped back into the aquarium. Some manufacturers market small internal wet-dry filters, which are intended for aquariums of a maximum volume of around 200 liters.

Here are the principle of Wet-dry filter placed under the aquarium:

Pump
Pumps are used for box or wet-dry filters. In the case of marine aquariums, they are sometimes used merely to circulate the water, or simply surrounded by a block of foam.

A pump's power
There are several brands of pump and various levels of power. The power level is calculated for the operation of a pump that does not raise the water level: the water is pumped and sent back to the same level. Manufacturers supply two figures for every pump:
- the maximum flow, which corresponds to a flow reversal height of 0;
- the maximum water height to which the pump can take the water, corresponding to a flow close to 0.

Filtering Media
The filtering materials can be either natural gravel, sand, clay, active carbon, peat, crushed oyster shells, rocks - or artificial - PVC, foam, Perlon, and various plastic materials.
Different materials correspond to specific functions.

For a coarse filtration, use gravel, rocks, sand, clay, or large pieces of PVC. A fine filtration requires fine sand, foam, or Perlon; a biological filtration, sand, foam, cotton, or clay. Peat, active carbon, crushed oyster shells, or calcareous rocks are effective materials for exerting a chemical action.

With the exception of the last category, a filtering material must be chemically neutral, i.e. it must not modify the main characteristics of the water (pH, hardness, or density).
All the filtering media of variable volume (gravel, sand, earth, clay) are easier to handle if they are placed in a fine-meshed pouch (made from a net curtain or tights, for example).

• Gravel and Thick Sand
These are used as pre-filtration media to trap the largest pieces of debris, especially in the external filters. They are being increasingly replaced by artificial material, but fairly thick sand (grains of 2-3 mm).

• Lava Rocks
These rocks, broken into pieces of various sizes, play a double role: mechanical, for suspended matter, and biological. The form and surface of the rocks encourage the presence of bacteria, as well as good water circulation of water.

• Oyster Sheik and Calcareous Rocks
These play the same role, but also release moderate amounts of calcium carbonate into the water going through them. They are therefore used to maintain a high degree of hardness in some types of tanks, such as regional East African aquariums, for instance. They must be pounded and crushed, and then rinsed carefully, in order to eliminate the fine particles produced.

• Clay
Clay, in the form of balls of a few mm to 1 cm in diameter, provides a good bacterial support. It is rarely used on its own, but rather as a complement to another material, to ensure pre-filtration.

• Peat
Peat is placed in a filter to acidify the water passing through it; therefore, its main role is not filtration, although it can trap some particles. Be aware that peat turns water an amber yellow color. It is, therefore, not at all advisable to apply peat designed for horticultural use, as it contains substances that can be dangerous in an aquarium. Suitable peat is commercially available, although you will have to proceed by trial and error and do some tests before finding the quantity needed to maintain a specific pH.

• Active Carbon
Active carbon is obtained by calcining (burning) vegetable matter under very precise conditions. It is a very porous material with properties useful to fish keepers. It fixes organic coloring substances, which makes it possible to obtain really clear water. It also fixes some medicines, especially those based on colorants. In this case, a filter is only used to eliminate a medicine, once the treatment has been completed. What is more, active carbon traps smells. Its main deficiency is that it loses these distinguishing properties quite quickly. It offers a good support for bacteria, but no more so than other more practical filtering media. To sum up, active carbon is a material with very specific applications, and not in saltwater.

• Perlon
This artificial material comes in the form of inter-twined filaments. Be careful: it must not be confused with glass wool, which is highly unsuitable for aquariums, as it can release tiny fragments into the water. It is generally used in association with foam as the first filtering material, especially so in box and wet-dry filters.

• Foam
This synthetic polyester foam has open pores, like that found in mattresses or cushions. This material is very fashionable in the aquarium trade these days and it seems to offer nothing but advantages: it is light, neutral, easy to handle and cut, as well as being cheap. Furthermore, it provides a highly effective bacterial support, and is also excellent for mechanical filtration.

The foam generally used has a density of 20 kg/m-\ and its porosity is ideal both for retaining suspended particles and for allowing bacteria to develop. Generally speaking, the experience of a great many aquarists and public aquariums has shown that a thickness of 8 cm, divided into two more or less equal parts for easier upkeep, is usually sufficient for filtration.lt is possible to find some commercially available, or else home-made, filters entirely composed of foam - small internal filters or external filters, both box and wet-dry - and these are also completely satisfactory.

• Various Plastic-Based Materials
Different types of plastic material, such as PVC, can be used to make the filtration or pre-filtration elements: small pieces of pipe around 1 cm in diameter, balls, cubes with an openwork design, etc. The list is endless, and contains not only items found in the aquarium trade but also recy-cled domestic materials.

• Combinations of Filtering Media
When several filtering materials are found in the same filter, the water must successively pass through materials decreasing in grain size. The coarsest materials serve as a pre-filter for large pieces of debris, while the others retain the finer particles. All these filtering media enhance the development of bacterial colonies that convert nitrogenous products, with pride of place being taken by foam and clay balls.

• Cleaning The Filtering Media
The filtering media progressively accumulate particles, at a rate depending on granule size, the speed at which the water flows through them and finally the amount of suspended matter it contains. When they are saturated, they can be cleaned with warm tap water, without any detergent or soap, until clear rinsing water is hence obtained.

Aquarists who have several tanks wash several pieces of foam together in a washing machine, though obviously without any washing powder. It is unfortunate that cleaning eliminates the large majority, or indeed all, of the useful bacteria. The filter will therefore be effective for particles but will no longer be able to play any biological role.

To alleviate this problem, you can clean only half the filtering media each time: the bacteria living in the unwashed part will be sufficient to purify the water and will quickly recolonize the other half. If you are using two filters, you can, of course, clean one at a time. If the aquarium has to remain empty, in the meantime the filtering media can be put into the filter of another aquarium, and in this way they will still collect bacteria and can quickly be put back into service. It is vital not to interrupt the nitrogen cycle in a biological filter, as this may give rise to toxic compounds.

Best Solution For Saltwater Aquarium Filtration
The ideal solution would be to use two filters: one with a moderate flow, mainly for the conversion of nitrogenous matter (a box or wet-dry filter), the other with a stronger flow, prizarily serving a mechanical function. An under-gravel filter can also be used to enhance the circulation of water in the generally fairly thick sediment, but it must not be used on its own. One effective combination consists of a reverse-flow under- gravel filter coupled with an external filter.

The filtration flow must be 3-5 times the volume of the tank per hour for fish, and up to 10 times the volume for invertebrates, especially Anthozoans. Once again, foam is the perfect material, providing it is no more than 6-8 cm thick. If thick materials, such as crushed oyster shells or PVC materials, are used, then the foam can be thicker. Never use peat or active carbon. Equipment specific to saltwater Marine fish are more sensitive to the quality of the water. This calls for the use of equipment to complement the filtration system, in order to obtain water of the highest quality.

• Reverse Flow Under–Gravel Filter

• The Protein Skimmer
This system enables the aquarist to carry out partial chemical purification of the water by eliminating certain dissolved substances, such as proteins. The principle is simple: the water is agitated in a confined space, leading to the precipitation of a number of substances. A frothy foam, often yellow-colored, is produced, and this is then eliminated via the overflow.

The protein skimmer is an independent element that can be placed anywhere in the tank. It can also complement the filtration system, reducing the burden of a box filter when it is installed in its first section. Also very often employed as a preventive measure in tanks containing fish, the protein skimmer is not used if the tank is not overloaded, and if a biological filter is already working effectively.

The protein skimmer is recommended for an invertebrate tank, especially one with corals and anemones, although it does eliminate some substances that are absorbed by invertebrates.
Aquariums of up to 300 liters use a protein skimmer fed by a fine-bubble diffuser, and therefore supported by an air pump. Beyond these volumes, plan on installing two protein skimmers, or invest in one fed by an electric injection pump.

• The Purifying Action of UV
Rays Ultraviolet rays are luminous, but invisible to the human eye. Some of them are responsible for tanning (UV A and B), while others, with a shorter wavelength (UV C), have germicidal properties and kill a large number of bacteria and viruses. These UV rays are used for the bacteriological purification of water, especially as their action is selective, as they do not destroy the "good" bacteria of the nitro- gen cycle.

The field of action of these rays is limited - somewhere in the order of a few centimeters. The water must therefore pass close to the source of the rays, at a speed which allows it to receive sufficient amounts of their luminosity. In order for the rays to exert their maximum effect, the water must be clear, and therefore well filtered. UV sterilizers are commercially available.

The lamp is completely watertight, thanks to a quartz sheath that allows this type of ray to pass through. The blue-violet color given off by the lamp only serves to show that it is functioning.

Do not look directly at the source of the UV rays, as they are dangerous for the eyes — this is why the sterilizer usually has an opaque covering. The lifespan of a lamp operating for 24 hours a day is around 5 or 6 months. However, the quality of the rays usually deteriorates after 4 months, and so they should be replaced three times a year.