The keeping of marine organisms in aquaria has come a long way in a remarkably short time. For example, successful spawnings of the various species of Clownfish (Amphiprion spp) no longer make headlines, although the achievement (rightly) continues to rate very highly in the eyes of most aquarists.

Yet, in spite of the spectacular progress that has been made, many people still feel that the marine hobby is so difficult and demands such high levels of expertise, that no-one but the dedicated specialist can ever hope to be a successful marine aquarist.

Experienced marine hobbyists, on the other hand, have been stressing for years that a sound, commonsense approach, coupled with a desire to seek correct advice and act upon it, is usually enough to set the beginner on his/her way.

There are three main types of marine aquaria:

native marine, housing species found around “home” coastlines;

invertebrate, containing species of marine organisms lacking internal skeletons;

tropical marine, a term commonly used when referring to aquaria housing tropical marine fish (even though an invertebrate aquarium may well be “tropical” in nature).

Each of the above categories requires a complete guide to itself to do it any justice. This particular guide, therefore, concentrates on just one category: setting up a basic marine fish tank.

Although it cannot hope to cover even this limited subject in great depth, it nevertheless attempts to tackle the main principles of this side of the hobby in sufficient detail to allow the potential marine aquarist to make an informed start.

Choosing The Aquarium

Choosing a suitable aquarium is one of the most fundamentally important decisions that need to be made. It is, therefore, well worth spending some time weighing up several possibilities before making a final choice.

As with the freshwater hobby there are two main points to consider: the type of aquarium and its size.

It must be stressed straightaway that some of the aquaria which can be used for freshwater fish are out of the question when it comes to marine organisms. The most obvious (and potentially lethal) are old angle-iron tanks. Iron reacts with both fresh and saltwater, but marine organisms are much more susceptible to the harmful effects of these chemical reactions than freshwater organisms are. Therefore, what would normally be a tolerable level of toxic substances in freshwater, is likely to be lethal in the marine aquaria.

The best way of avoiding this is, clearly to give this type of aquarium a miss and opt for a safer one instead. This can actually be an angle-iron tank which has been coated in such a way that there is no direct contact between the metal and the water. PVC is one such suitable coating, but there are others as well.

Plastic or Perspex aquaria obviously do not present any of the above problems. They also have the added advantages of being relatively light and inexpensive. However, counter-acting this, there are several disadvantages, such as the discoloring that occurs with age and the ease with which plastic scratches, thus spoiling the appearance of the aquarium as a whole.

The most popular aquaria today are those made entirely of glass. Their advantages are numerous, including ease of construction. This has been made possible by the development of silicone-based aquarium sealants which set in a few hours but can last, without leaks, for ten years or more.

The flexibility that this major development has brought to aquarium construction has led to all-glass aquaria of sizes, prices and shapes (including cylindrical ones) to suit virtually every conceivable need and pocket. The ease with which many of the basic shapes can be constructed has also resulted in a higher incidence of home-built aquaria, particularly amongst specialist fishkeepers.

Each tube of sealant carries full instructions, so I will not take this matter further other than to stress that tanks measuring 3ft. (90 cm.) or more in length should carry at least one front-to-back strut to prevent bowing and possible disaster.

Although the range of aquarium types discussed above is not fully exhaustive, it includes those most commonly met. In addition, there are stainless steel, anodised aluminium, glass-fronted fibreglass and other types of aquaria, but space does not allow fuller consideration of these here.

Aquarium Size

However large an aquarium may be, it is still minute when compared to the natural environment in which fish normally exist. Therefore, no matter how careful or experienced an aquarist may be, conditions inside an aquarium will inevitably be artificial, to a greater or lesser extent.

As a consequence of this, there will be a build-up of certain substances and a possible lack of others which can cause serious problems if the maintenance routine is inadequate.
One factor that will help or hinder the development of an adequate routine is the size of the aquarium. The reason for this is that the smaller the volume of water present, the more susceptible it is to changes. Therefore, even a minimal amount of overfeeding will lead to serious pollution in a small aquarium.

In a large one, its effects are proportionately less and should, at least, give the aquarist the margin of safety required to remedy the problem before it really gets out of hand.

Although this principle applies to both freshwater and marine aquaria, its significance is considerably greater in the latter because marine organisms are much more sensitive to water quality changes.

It, therefore, makes sense to for the beginner to setup the largest aquarium possible from the start. The extra expense involved will more than pay for itself in a short time, simply by the number of expensive problems that will be avoided.

In any case, a 36″‘x 15″ x 12″ (90 x 38 x 30 cm) tank should be considered the minimum by anyone who has not kept marine fish before. Experienced aquarists can go below this without courting disaster, but not the beginner, unless (s)he is lucky or a very fast learner.

Aquarium Covers

There is a wide range of aquarium hoods on the market, ranging from simple covers to sophisticated, partitioned units designed to house lighting and other equipment. It is really up to the aquarist to decide which of the available models best suit his/her needs.

Two points, though, are worth bearing in mind. First, it is essential that there are no exposed metal parts. If there are, they will react with the saltwater and will cause, at best, distress to the fish and, at worst, their death. This can be avoided by painting the exposed metal with a non-toxic gloss paint. If this is done, several days, at least, should be allowed for the paint to dry out thoroughly.

The second point referred to above concerns evaporation and splashing of water. Both are unavoidable, particularly since aeration is usually quite vigorous in marine aquaria.

The easiest way to avoid these potential problems when setting up your tank is simply by using a condensation or cover sheet. These can be bought ready-made in plastic or can be made out of a sheet of glass cut to a size slightly smaller than the tank itself. by supporting this sheet either with glued-on strips of glass or by resting it on the back-to-front struts mentioned in an earlier section, the water will drop back into the aquarium without making contact with the hood, frame or sides.

Water Quality

Whereas one can get away to an extent, with a certain degree of deterioration in water quality in freshwater, the same cannot be said of marine aquaria.

As I have mentioned earlier, marine fish are very sensitive to chemicals in the water. Some of these can be introduced by the aquarist while others are produced by the fish themselves. Of the latter, the two most toxic ones are Ammonia and various Nitrites which can prove lethal even at very low concentrations. Maintenance of good water quality is, therefore, an absolute must in marine aquaria and the aquarist who ignores this does so at his/her own peril. The collection of seawater must be avoided, not because it is harmful in any way (!) but, rather, because it soon becomes “imbalanced” in the confines of an aquarium and can cause all sorts of problems through the introduction of unwanted micro-organisms, such as pathogenic (disease-causing) bacteria.

The following are the most significant aspects of water chemistry that need to be appreciated before a start in the marine hobby is made:

Specific Gravity, Salts and Trace Elements

Saltwater, as the name implies, carries a number of chemicals dissolved in pure water. These chemicals make the water heavier, or denser, and it is the way in which this compares to the weight of pure water at 40C that gives’ the figure referred to as Specific Gravity.

Saltwater from seas in which “aquarium” species of fish are found can vary from 1.020 (in parts of, e.g. the Pacific) up to as much as 1.035 (Red Sea). Most seas, however, have a S.G. value of between 1.020 and 1.022. While keeping fish in water having a higher than recommended S.G. will have deleterious effects on them in the long run, fish kept under lower S.G. conditions (provided the change is carried out gradually) can adjust and often live longer. In the aquarium, a range. between 1.020 and 1.023 is suitable for most species. This value is achieved by dissolving balanced, prepared aquarium salt mixes in the recommended amounts of water (tap water is adequate – you do not need to use pure water), and measuring the S.G. with a hydrometer.

Hydrometers are calibrated to give readings at the range of temperatures at which most tropical species are kept, i.e. around 24-260C (approx. 75~80 deg.). Aeration helps the salts to dissolve so this should be provided, particularly when time is short.
Many of the salt mixes available also contain all the essential trace elements which fish and other organisms require. This should, therefore, be checked beforehand and provided as a supplement if required.

Ammonia, Nitrites and Nitrates

These three chemicals, despite some differences, all have one thing in common: Nitrogen.

For this reason, they are usually considered together as part of the Nitrogen Cycle. Basically they relate to each other as follows:

Fish and other marine organisms break down protein as part of their normal digestive processes. Some of the nitrogen contained in the proteins is retained but the rest will be eliminated as Ammonia. This substance is highly toxic but is soon converted in a balanced aquarium into Nitrites by the action of bacteria, e.g. Nitrosomonas. Unfortunately Nitrites are also toxic, but other bacteria, e.g. Nitrobacter; convert the Nitrites to Nitrates which are considerably less harmful. Some of the Nitrates can be converted into free Nitrogen while some will be assimilated by plants and algae. If these are eaten directly by fish, or indirectly by fish feeding on other animals which, in turn, have fed on the plants, the cycle will have been completed.

Clearly it is essential to keep the Nitrogen Cycle under control, with Nitrite readings at, or near, zero. This can be achieved in a number of ways, most of which involve some form of filtration (see section on Aeration and Filtration).

pH – Acidity and Alkalinity

Pure water is said to be neutral and is given a pH value of 7. Lower figures represent progressively higher degrees of acidity while higher figures represent higher degrees of alkalinity.

The complete scale runs from 0 to 14. However, it is not a linear cycle, it is logarithmic. This means that water at pH 8 is 10 times as alkaline as water at pH 7 A reading of pH 9 indicates, therefore, 10 times the alkalinity of water at pH 8 and 100 times that of water at pH 7.

This explains why even small changes in pH can have such dramatic effects, particularly if the changes are abrupt and do not give the fish a chance to adapt. The pH range for tropical marine tanks should be between 8.0 and 8.3, i.e. alkaline. This can be measured (as is the case for Nitrites) by means of reliable, inexpensive test kits. The addition of a buffer solution will help prevent abrupt fluctuations in pH and should be considered as a useful part of every aquarist’s tool box.

Aeration and filtration

Aeration and filtration systems vary so much in design, complexity and price that it would be impossible to present a comprehensive review here. Basically they all aim at oxygenating the water and reducing or eliminating toxic wastes from it.

Although some toxic wastes (such as Ammonia and Nitrites) occur in solution, others occur as actual particles. This applies in particular to faeces (“droppings”). Clearly at least two types of filtration are required: (a) mechanical, to remove the debris and (b) biological (or biochemical) to remove the rest. Many of the filtration systems that are available today can do both jobs, and aerate the water, all at the same time.

Box filters

These channel water either under the influence of an air stream from an aerator or a water current from a motor, through a box which can be internal or external to the aquarium. In this box, various “sandwiches” of filtering medium can be arranged, e.g. filter wool, charcoal, gravel/shells, or even diatomaceous earth.

Box filters are used primarily for mechanical and/or chemical filtration.

Undergravel filters

These consist of a specially designed plate which is placed under the gravel and one or more air-lift tubes into which are introduced air lines connected to the aerator (pump). As the bubbles of air rise, they lift water up these tubes and drag water from the aquarium down through the filter plates. If these plates are covered with a suitable medium on which the beneficial Nitrosomonas and Nitrobacter bacteria can grow, then the water will be purified as it flows through.

A suitable medium (substratum) for this is either a mixture of crushed shells and coral sand, or layers of these, made up of one part of shell to two parts of sand. The depth of this layer is also important – anything less than 3 inches (ca. 8 cm) will not be fully effective. The chemical composition of the shells and coral sand also help maintain the pH in the required region of 8.0 to 8.3.

As the air bubbles out at the top of the air-lifts, aeration occurs. However, if the bubbles are large (rather than a “mist”) or if the aerator is not strong enough, then supplementary aeration by means of diffuser stones must be provided.

Reverse flow filtration

This system is similar to undergravel filtration in that it uses the substratum as the filter medium. However, in reverse-flow filtration, water is forced down the air-lifts by means of a power head, power filter outlet or pump, and up through the gravel. One advantage claimed for this method is that the water can be mechanically filtered before it reaches the gravel whereas, in normal undergravel filtration, the gravel itself has to do this job.
If reverse-flow filtration is used, then aeration does not occur to the same degree and a separate aerator must, therefore, be used.

Power filtration

Power filtration can have all (or most) of the advantages of undergravel filtration, plus several others. For example, regular cleaning is easy and a range of filter media can be used, e.g. charcoal, filter wool, foam, shells, etc. In addition, faster flow rates allow for a vigorous circulation of water which, when combined to a spray-bar attachment, ensures efficient aeration without the need for a supplementary air pump.
One disadvantage of power filters is that they do not normally harbour as many beneficial bacteria as undergravel filters. Therefore, if the aquarium is fully stocked, there is a possibility that further water purification may be necessary. Regular monitoring of water quality by the use of test kits will soon show if this is the case. This supplementary equipment can take the form of an Ozonizer, and Ultra-violet Sterilizer or a Protein Skimmer.

Ozonizers, Ultra-violet Sterilizers and Protein Skimmers

Ozonizers are useful in that they can restrict/control the growth of bacteria. They may also help in controlling certain diseases. Overdoses will cause serious problems.

Ultra-violet Sterilizers will kill bacteria if used in sufficient doses. It is also claimed that they will control algae, fungi and several pathogenic organisms.

Protein Skimmers produce a foam which is capable of collecting organic matter in an easy-to-clean trap. When combined to an Ozonizer efficiency is improved even further.

Combined filtration System

Protein skimming, mechanical filtration, biochemical filtration and aeration are all combined in a sophisticated, effective but expensive system which has become available in recent years. The aquarist must, of course, make up his/her own mind, particularly since there are other expenses to be considered when first setting up, and other filtration/aeration systems are also highly effective when properly managed. Whichever system is adopted, one should aim for a turnover rate of around three times the capacity of the aquarium every hour

Temperature Control

Most of the commonly available marine fish are at their best at temperatures between the mid- and high 70ºs F (24º-26º C). Although this temperature can be allowed to fluctuate slightly these fluctuations must be gradual. Sudden changes in temperature can cause similar problems to sudden fluctuations in pH, as mentioned earlier.

The easiest method of heating an aquarium is by means of combined heater/ thermostats. This is not the only way of course, but it does have one outstanding advantage over other methods in that it is very easy to set up.

Separate heaters and thermostats of various designs are also available. One of their advantages over combined units is that individual components can be replaced more easily. Separate units also make it possible to operate more than one heater from a single thermostat. In some cases, the savings thus made can be significant.

When calculating the heating requirement for an aquarium, allowances should be made for major drops in external (room) temperature. If the wattage of the heater chosen is approximately twice the figure arrived at through strict mathematical calculations, this will provide sufficient reserve power to cope with most situations. Adopting this approach, one can arrive at a reasonable wattage by applying the following rule-of-thumb:- For tanks measuring approximately 24″ x 12″ x 12″ allow 10 watts/gallon For tanks up to 48″ long, allow 6 watts/gallon For tanks up to 72″ long, allow 4 watts/gallon


Aquarium Size/Wattage:

  • 24x12x12/75-100W
  • 36x15x12/100-150W
  • 48x15x12/120-180W
  • 60x 18x 18/150-210W
  • 72 x 18 x 18/ 200-300W

Aquarium Lighting

Aquarium lighting usually receives a great deal of attention where freshwater aquaria are concerned. However, when it comes to marine aquaria, this subject is often given no more than superficial treatment. Perhaps the fact that few, if any marine plants are cultivated by most hobbyists has something to do with this.

Indeed, if the tank is to contain just fish, and if the aquarist dislikes seeing algal growth on the rocks and sides of the aquarium, then reduced light intensities will serve both aims satisfactorily. However, it must be stressed that those fish which like/require/prefer algae in their diet must have this (or an equivalent) otherwise provided. Aquarian Vegetable Diet is an ideal source of high-quality vegetable food.

There are two main forms of saltwater aquarium lighting: tungsten and fluorescent. Recently high-pressure mercury vapour lights have also become available. Each of these has its own advantages/disadvantages and the aquarist must weigh these up before coming to a final conclusion.

Tungsten bulbs are cheap but hot and do not enhance the appearance of the fish as much as fluorescent tubes do. They do, however, produce light relatively rich in red wavelengths which are beneficial to the growth of green seaweeds.

Fluorescent tubes exist in a number of types, each emitting its own range of wavelengths from brilliant white to deep purple. If red or brown algae are being cultivated, then those tubes emitting light close to the blue end of the spectrum will be found more suitable.

Mercury bulbs produce light of high intensity and are, therefore, particularly suitable for deep tanks or for those where good algal growth is essential. These bulbs are, however, expensive to install but are long-lasting and relatively cheap to run.

Assuming that the lights will be switched on for an average of 14 hours per day the following table may be used as a rough guide for fluorescent tube illumination. With marine aquaria, some experimentation is almost always necessary in order to establish adequate lighting levels to suit individual aquaria.

Approximate total wattage:

Tank Dimensions. For viewing only. For algal growth

  • 24x12x12 – 30w – 60w
  • 36x15x12 – 40w – 90w
  • 48x15x12 – 60w – 120w
  • 60x18x18 – 140w – 220w
  • 72x18x18 – 160w – 270w

Wherever possible, the above wattages should be divided equally among several tubes, for evenness of distribution. This also allows for combinations of tubes emitting different types of light.

Other Aquarium Requirements

In addition to the items mentioned in the previous sections, there are several other musts you should consider in your marine aquarium setup:

Nets, replacement heater/stats (wired up and ready to use at a moment’s notice), thermometers, algae scrapers, siphon tubes, “spot” cleaners, e.g. aquarium vacuum, long forceps (for removing objects, dead fish, etc.), plastic buckets (for water changes), glass jars (for equilibrating temperatures prior to introduction), spare diaphragms (for aerators), etc. will all make life easier.

A selection of test kits, to include Water Hardness, pH and Specific Gravity should also be considered essential.

Foods and Feeding

Good quality commercially prepared foods, such as Aquarian, contain very little moisture and very high levels of nutrients. Therefore, a little of this food goes a long way. Some aquarists overlook this fundamental point and overfeed their fish. The results are, invariably disastrous.

Food should be consumed within a few minutes. If uneaten flakes can still be seen after, say ten minutes, then the fish have definitely been overfed. It is worth noting that it is far more difficult to underfeed than overfeed, so it is best to start off with very small feeds and increase these gradually until an optimum level is reached. Two small feeds per day should be sufficient.

Some marine fish can be a bit awkward at first but we have found at Aquarian (in laboratory controlled trials) that flake food is readily taken as long as it has been prepared from all-fresh ingredients, such as whole fish, minced beef or liver, or (even) rabbit. Aquarian Marine Flake contains four all-fresh ingredient flakes, plus a black vitamin and mineral flake and a green seaweed flake. Most of the other flaked foods in the Aquarian range are also avidly taken by tropical marine fish and Aquarian Vegetable Diet should be considered essential for all those marine species which require algae as part of their food. Aquarian Pacific Shrimp is a particularly good food to offer all marine fish are a regular treat.

Live foods (with two exceptions) are best kept out of the marine aquarium because of the risks of introducing pathogenic organisms; also most of the commoner types of live food are fresh-water in origin and die very quickly with awkward consequences.
The two safe ones are Brine Shrimp (newly-hatched or adult) and chopped, clean, earthworms. Even earthworms need to be treated with caution, with all uneaten bits being removed after a short time. .

Filling and Stocking the Aquarium

Synthetic salt mixes carry full instructions on mixing and these must be followed to the letter to avoid problems later on.

Before placing any water (pre-mixed or otherwise) in the aquarium, the undergravel filter with its air-lifts, plus the coral sand and shell mixture/layers must be in place. At this stage, no electrical equipment is either installed on switched on.

If the salts are going to be mixed with the water inside the aquarium (instead of in a plastic bucket or other container), then it is best to do this after half the water has been added. Once the tank is half full, the complete salt complement is put in and the tank is then filled to within an inch or so from the top. At this point, the heater/stat is placed into position and switched on, along with the aerator and undergravel filter (power filtration is unnecessary at this early stage).

The aquarium can now be left with all systems running for about 24 hours by which time, the salts will have dissolved completely. Specific Gravity is then checked and altered if necessary by addition of more salt (to raise the S.G..) or by the replacement of some of the aquarium water with tap water (to lower the S. G. ).

Although the tank may be balanced in terms of temperature, pH, hardness and S.G., it is far too raw at this stage to accommodate any fish. The maturing process may be speeded up considerably by the addition of special water treatments that have been developed specifically for this purpose and by leaving the lights on all the time. Over the next fortnight or so, the Nitrite level should first increase well beyond the tolerance limit of most fish and then drop to around zero. When this is achieved (and assuming that pH is between 8.0 and 8.3), conditions should be suitable for the first fish to be introduced. Power filtration and/or “charcoal” (chemical filtration) can now be put into operation. Saltwater holds considerably less oxygen than freshwater. This, added to the high sensitivity of marine fish to environmental conditions, means that only relatively low numbers of fish can be kept in tropical marine aquaria. One other factor to bear in mind is that it takes anything up to six months for a marine aquarium to mature fully. Therefore, until this happens, the stocking density should be kept to around 50 percent.


No. of fish approx. 2″ long:
Surface Dimensions(inches) New tank Established tank
24×12 3 6 (This size nor recommended for beginners)
36×12 4 9
48×12 6 12
60×18 11 22
72×18 14 28
When introducing fish, temperatures must be equilibrated by floating the bag in the tank for about fifteen minutes. If at all possible, debagging should occur in subdued light and no food should be offered for at least several hours.

Quarantine and Diseases

A new tank with its collection of fishes will inevitably act as a quarantine tank. However, later additions should be kept for at least a fortnight in isolation in a separate tank, until all risk of disease has passed. The expense involved in setting up this tank will more than pay for itself in a very short time.
Even when precautions are taken, fish may succumb to disease from time to time, but it must be stressed that, despite the distressing effects that diseases can have, most are easy to prevent through proper water management, reasonable stocking, etc. In addition, marine fish are generally quite resistant to disease and outbreaks should, therefore, be infrequent.

Routine Maintenance

Every aquarist soon develops a maintenance regime suited to his circumstances, such as time availability numbers and sizes of aquaria, numbers, sizes and types of fish, etc. However, every program should include the following:


Check on temperature; state of health of fish; feed fish in the morning and early evening; switch tank lights off ten minutes before room lights.


Check specific gravity pH, hardness and nitrite levels; check heater/stats for leakage; check on supplies of food and remedies; top up tank with tap water if necessary Every three to four weeks Clean out box, power and sponge filters; clean cover glass, scrape algae off sides of tank if necessary; check aerator and lighting equipment.
Every four to six weeks Gently stir topmost layer of coral sand or gravel; allow mulm to settle and then remove with siphon tube; carry out a 20-25% water change; prepare the new water 24 hours in advance, aerate it vigorously and check all parameters before adding to main tank.

A note about fish

The tropical marine hobby is expanding very quickly. As it does so, more and more exotic species become available. Often, little is known about their ease/difficulty of maintenance in aquaria. If one is starting up as a marine aquarist, it is, therefore, advisable to steer clear of difficult, unknown and expensive species. There is enough colour and interest among the tried-and-tested ones to provide both great enjoyment and realistic challenges for months, or even years.