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Tuatara: Volume 4, Issue 3, September 1952

Design and Maintenance of Marine Aquaria

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Design and Maintenance of Marine Aquaria

The rich varied fauna of our sea-shore is a stimulus to the setting-up of marine aquaria. This is a simple task provided certain fundamentals are recognised and practised. The maintenance of marine aquaria is complicated by the corrosive action of the water, by the necessity of retaining a uniform and normal salinity, and by the fact that marine plants do not survive readily in aquaria. The latter places a relatively early limit on the life of a marine aquarium. The constant addition of food leads finally to over-fertilization of the water which starts blooms of diatoms, algae, etc. These rob the water of essential minerals, disturb the ionic balance and in brief ‘spoil’ the tank which must then be emptied, cleaned and refilled with new water. Under proper management this cycle runs two to three years, in constrast to the freshwater tank which can be kept in operation for twenty years and more without a change of water.

The operation of large-scale marine public aquaria is based on water-circulation, filtration, replenishment, and light control. Natural sea-water is drawn from storage tanks, aerated, supplied to the display tanks, run off from these to sand filters, and back to storage. The removal of sludge from the filters can be used to keep down the increasing fertility of the water, while the decay of animal and plant material in the filter returns minerals to the water, maintains salinity and ionic balance. Blooms of microscopic plants are avoided by reducing the light coming to the tanks. Such techniques generally have been unattainable for small aquaria but we have recently developed in our laboratory a simple device which offers a practical system of filtration and circulation.

Small marine aquaria can be set up and maintained for several years without aeration or circulation, but the display of animals is limited in number and variety. Many of the basic principles for such static tanks are common to circulation tanks. Always select the largest possible tank. There is an unknown factor in tank management, long believed related to temperature stability, but certainly related to the size of the tank. The difficulties of keeping aquatic animals diminish with increase in size of the the tank. A tank for permanent display should be not less than ten gallons capacity, and the larger than this, the better. Success can be obtained with small tanks, but large tanks are easier to establish and maintain.

Shape is equally important. Gas exchange can occur only at the surface and the ‘surface/volume’ ratio should be strongly in favour of surface. page 88 In large tanks, one square foot of surface for each eight gallons is a fairly good guide. Aeration is no corrective for a limited surface since if the population is dependent on aeration, it will suffocate if the aerators fail. In our laboratory we are finding satisfactory even with irregular power supply tanks 5 feet long by 1 foot wide and 1 foot deep. These are filled to a depth of 10 inches.

Construction of marine tanks aims at keeping salt water away from metal. This suggests an all-glass tank, but these are cast and optically defective. Flaws and runs in the glass distort the view and ruin the display. Using the dimensions given above, our tanks (Fig. 1) have an angle-iron frame of 1½ or 2 inches by ½-inch angle made into a rectangle to which is welded a 10-inch angle-iron upright at each corner. One or two flat straps welded across the bottom give useful strength. The glass is quarter-plate, bottom, ends and sides, although the ends can be ‘double diamond’ if desired. The sides and ends are a full 12 inches high so that the uprights fall short of the top by an inch. The assembled frame is painted with duco before glasing using ‘Vulcatex’, a proprietory non-hardening putty which does not yield under slight torsion of the frame. The tank is covered with heavy window-glass which rests entirely on the quarter-plate ends and sides and so keeps water away from the metal of the frame. Materials for a 5-foot tank cost about £12.

A tank of this size and shape can be maintained as a static tank, i.e. without circulation or aeration, and with careful management will hold animals for two or three years without a change of water. Mount the tank on a firm support, away from direct sunlight and for preference on a side of the room remote from the windows. Where this is not possible, place the tank with one end towards the window. A bottom of coarse gravel should be provided so that faeces and other debris can sink between the pebbles where bacterial activity will quickly break them down. Mark the level of the water when the tank is first set up, and maintain this level by adding only distilled water, and that only gradually. Let the tank stand for at least a fortnight after filling and before introducing the animals. During this time there will probably be minor blooms of bacteria and protozoa which will cloud the water and may diminish the oxygen content to an extent that any animals in the tank would suffocate.

Animals for a static tank should be collected from a rock pool at high tide level. The tank described above will carry three or four crabs, several medium leather-stars, several hermit crabs, winkles, rock-pool shrimps and page break
Legend to Figures Fig. 1: General lay-out of metal-framed tank suitable for marine aquaria. The tank can be reduced to a length of 3 ft. if a smaller tank is desired. Fig. 2: ‘B’-type all-glass device for circulating water in marine aquaria. Fig. 3: ‘R’-type all-glass circulating and filtering device. The dimensions given are for a tank having a 12 in. side and filled to 10 in. The air-entry tube fits over a corner of the tank.

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page 90 fish. The latter in swimming give some minor circulation to the water which aids gas exchange. Other animals can be tried, but do not overcrowd the tank in the first instance, rather build up the community slowly.

Simple aeration has little value from the viewpoint of oxygenation of water in a properly set up tank. Its function is to establish a circulation of water, but the bursting of the bubbles at the surface splatters salt water on to the cover over the tank where it evaporates leaving the salts behind. Over a period this can actually lower the salinity in the tank. This can be prevented by the use of one or other of the circulators which have been developed here. The ‘B-type’ device shown in Fig. 2 was brought to its final design by Mr. R. Barbour, Glass-blower at this College, and is a compact, efficient and sturdy pattern. The second, the ‘R-type’ (Fig. 3), carries out both circulation and filtration. The filter-chamber is very loosely charged with washed glass wool which traps faeces, diatoms, and other organisms. This glass wool can be changed from time to time as it clogs, and so used to prevent excess fertilization of the water. Two circulators, one at either end of a five-foot tank, provide an ample circulation of water without the troubles rising from direct aeration and without accelerating evaporation. The circulators are suspended in the tank at the corner, and fit beneath the cover. Cut off the corner of the cover so that it fits closely around the air-entry pipe.

The circulators are supplied with air from ‘S.S.’ brand aerators, one of which can supply five circulators. These aerators are inexpensive, simple and in our experience rugged and reliable.

A tank with circulation will carry a more varied and numerous community than a static tank. Anemones, brittle-stars, sea-worms, flat-worms and practically any of the inshore fauna can be maintained. Our tanks now hold two small sharks. Mantis-shrimp trawled from forty fathoms have lived for four months; but such fragile forms as Obelia have not been established. Food is finely chopped beef, liver, fish, and in feeding there is the cardinal rule: feed as little as necessary to keep the animals in health and remove uneaten food promptly.

Management of the established aquarium is not difficult. Keep the glass and frame free from saltwater to maintain visibility and prevent corrosion. If it is necessary to interfere in the tank never use metal instruments. Use clean hands or wooden tongs. Do everything possible to prevent accidental loss of seawater, and make such loss good with more seawater, which can be stored indefinitely in stoppered glass bottles preferably held in the dark. Watch the tank for the first signs of blooms of microscopic plants, and if these commence, reduce the light.

With care it is possible to keep marine aquaria even remote from the sea. In Wellington, we have ready access to the sea but with ordinary care we have maintained small static marine aquaria for three years without change of water, elsewhere I have used one lot of seawater for seven years.