A LARGE AND INTERESTING REEF-AQUARIUM IN OSLO

By Alf Jacob Nilsen, Norway

This article is reprinted with permission from Das Aquarium

Usually the modern, private owned marine aquariums contain up to a thousand litres of water with a standard decoration and a regular rectangular shape. The technique of the modern reef aquarium is well known in Europe, and our tanks are not very different technically. It is, however, different what shape and size is concerned, and since the whole system has been working well since the very beginning, it is worth talking about in an article.

The idea of this large and rather unusual reef-aquarium was created by Mr. Ingar Gulbarndsen - who is the owner of the tank. All the biological and technical planning and design has been done by "Bioquatic" - the authors small firm which has specialised in constructing and designing coral reef tanks.

The Idea

We wanted to create something new and try to achieve an effect of an reef-cleft that stretched far backwards and gave an impression of "infinity". We wanted to build an aquarium with a depth that would shock visitors and where "new" organisms could be detected even after having viewed the tank for hours.

In other words; to make an aquarium that was a contrast to what have been made in Scandinavia earlier.

To achieve this we planned the depth to be 250 cm with another 50 cm behind the back-window. The wide was set to 180 cm and the height to 100 cm, fig. 1

The Construction

The platform was build out of wood upon which a 20mm plywood was mounted and covered with 10mm thick styrofoam. The aquarium itself was build from plywood reinforced with several layers of polyester and sealed with black top-coat painting. In the top-front and top-back, an iron-girder sealed with polyester and top-coat made a strong and stable support for the upper edge of both windows. The 15mm thick glasses were mounted with silicone and a 10 cm silicone support was used on all edges. The silicone was allowed to dry for a week.

In any reef-tank it is advisable to let surface water enter the skimmers. For this reason the surface-layer must flow into a chamber and from here be pumped into the skimmers. We did prepare a sufficient cut in the tank for the run-off of water. This run-off-cut should be made as wide as possible. The water enters a glass aquarium of app. 150 litres through a box of perforated PVC-sheets which very efficient catch fish, crustaceans and other animals that overflows together with the water. This space does also houses electrodes, a heater and acts as a place to store Artemia in a special cylinder if needed.

The use of plywood, polyester and top-coat are ideal and perhaps the only wise materials to use in large reef-aquarium. We have never detected any negative effect with them. Although they smell heavily in the beginning, once hardened they become very strong and easy to work with.

After the aquarium had dried and the work with polyester was finished, we glued several perforated PVC-tubes inside on the sidewalls. They were later to be used when live rocks should be mounted. We did also install outlet tubes for circulation among others some that would allow sufficient circulation behind the decorations.

To avoid chaos, tubes taking the water to and from the filter units were led below the floor. This later turned out to be a very good and practical idea. One must, however, be sure that there is no leakage.

The filter system The main units in the filter systems are three large "Bioquatic M110" skimmers. The water is pumped by an EHEIM model 1042 giving 5400 l/h. 3300 l/h flows through a small mechanical filter (cleaned every other day) and then enters two skimmers mounted in series. The rest flows though one skimmer, a unit with activated carbon and an UV-C sterilizer. The skimmers are constructed in order to remove as much organic as possible. Sufficient air is provided by a compressor mounted in the near by garage . All skimmers are cleaned twice a week. To maintain the water as poor in nutrient as possible was most important to us ! Not all organic can be removed by skimming. The carbon unit contains app. 2 kilos of Hydra Carbon, making it to an very active absorbing filter that keeps the water free from "yellow compounds" and makes the water look crystal clear. An electronic flow-meter indicates when the flow through the carbon unit decreases due to the gathering of organic. Normally the carbon is changed every six-eight weeks. In series with the absorbing filter is a 30W ultra- violet sterilisator and another skimmer. The water is returned to the far side of the aquarium through two 75mm PVC-pipes.

One should note that no outside biological filter is used. The only biological filter is the decoration consisting of more than 600 kilos of live rocks. So far we have not been able to measure any amount of NO ³ and NO ² by the use of a commercial test kit from Merck.

To maintain the buffer capacity and to ensure the adding of calcium are also of the greatest importance in any reef aquarium. We have with this large tank used a "Bioquatic Calcareous Reactor" as described in box 1.

The Calcareous Reactor

The adding of calcareous water refills both calcium (Ca ⁺⁺ ), which is important for all calcifying animals, and bicarbonate (HCO ³ -), which is important in order to maintain the buffer capacity.

When calcareous water is mixed, either from clumpy Calcium oxide (CaO) or from the more powdery calcium hydroxide (Ca(OH) ² , eventually calcium-hydrogen- carbonate (Ca(HCO) ³ ) ² ) will form as shown in this reaction:

CaO + H ² O Ca(OH) ² + ENERGY + CO ² Ca(HCO ³ ) ²

The calcium-hydrogen-carbonate dissociates into Ca++ and 2HCO ³ - ions. The contents of hydrogencarbonate can be measured by measuring the carbonate hardness (dKH) which should be very high. However, this is not a very stable situation and if the calcareous water is stored for a week or so, the reaction seems to shift to the left and the calcareous water becomes lower in hydrogencarbonate.

To increase the stability of the calcareous water, I have developed a calcareous reactor which consists of:

a) A reactor formed as a cylinder with a volume of 20 litre and mounted beside the aquarium.

b) A peristatic pump (2 l/hour) with a level sensor, the latter mounted in the aquarium.

c) A magnetic stirrer mounted below the reactor and a stirring pin inside the reactor

The idea is to mix calcium hydroxide with water once a day in order to some extent prevent the reaction to shift to the left. This is done by the magnetic spinner coupled to a timer. When water evaporates from the aquarium the level-sensor turns the peristatic pump to "on" and freshwater (free from algae nutrients) is pumped into the top of the reactor. The water level in the reactor rises and calcareous water overflows into the aquarium through a pipe leading 2/3 down in the reactor. This means that freshwater enters the reactor at the top while calcareous water from the bottom of the reactor refills the aquarium.

I have calculated the amount of calcium oxide needed for each litre water that evaporates from my aquarium, and found this amount to be 1.0 gram. From time to time the reactor should be cleaned with a weak acid and then properly rinsed with water.

Mr. Gulbrandsen has designed an elegant way of automatically adding solid Ca(OH) ² into the reactor each day by the use of a old coffee- and soup machine. About 20 grams Ca(OH) ² are used every day. The amount is added as soon as the stirrer starts for a few minutes every evening. As much as 25 litres of waters evaporates each day which is all replaced with high-quality-calcareous-water through the reactor. As the pH of the calcareous water is close to 12.0 this will, if no action is taken, result in an severe increasing of pH. The pH is, however, controlled to an upper limit of 8.50 by the automatic supply of CO ² through a "Futura Aquaristic Computer". The computer does also control temperature and some of the pumps used for circulation. Beside this it continuously measure pH, salinity, temperature and the redox value. It is "a must" for a large reef-tank.

In Norway the concentration of silitium as silicate in the freshwater can be very high and will, unless removed, course an explosive growth of diatomea. For this reason we prepare the water used for mixing calcareous water through an HW S30-Osmosis equipment.

Inside the aquarium we would have wanted a wave-movement of water, but unfortunately this could not be made be course of limited space. instead two Eheim 1042 each giving 5400 l/h was used to make an alternating stream of water along the decoration. Together with them several smaller pumps (Sacem "Galaxy" and Turbelle T4002) were mounted. All in all the circulation is great, but this is perhaps the technical part that could be improved by the use of one or two more powerful pumps or even a wave-generator.

The Illumination

If one want to keep hermatypic corals and other organisms containing symbiotic algae, light is a most important factor. We have chosen the Metal hallide lamp "Berliner Model" which is well known to German aquarists. 7 lamps of 250 W/D each are installed and combined with them are three Phillips TL03/40W (blue) light tubes. To achieve a special aesthetic effect a disco-bulb and a spotlight is used to reflect beams on the curved, blue plexi-slide which is placed behind the back-window. A few other spotlights are also used to simulate a sunset and go on just before the main lamps begin to close. To view the aquarium around midnight when the shadows begin to fall and "sunset" appears, is an marvellous event. One can clearly observe how life in the aquarium changes together with the decreasing light.

The Decoration

The decoration plays a major role in the aesthetic effect of this aquarium. When live rocks are used, a very common mistake is to place them as a pile of rock with no "open space" in between which will give the impression of a rather dull aquarium. We planned the decoration in detail and tried to follow our planning when the 600 kilo of live rocks were placed. The rocks were imported from Indonesia and "large pieces" were ordered. To build a decoration from live rocks makes the aquarium look almost like a true reef, and our large tank this effect was most impressive. For years we will be able to detect "new" and interesting organisms popping up from the stones, and although there is a risk that a few coral- and even fish eating, animals are introduced, the positive effects from the rocks are far greater than the negative. The rocks are by no doubt playing a major part in the maintenance of a low level of nutrient in the aquarium. It is, however, very important not to rush, but give the rocks plenty of time to settle down and to let a diverse and rich fauna of bacteria develop before many fish and corals are introduced. To overlook the importance of just this is another very common mistake in Skandinavia reef aquaristic today !

Before the decoration could be built it was necessary to prepare seawater. We used natural seawater, collected at "Moss Biological Station" in the Oslo-fjord, as well as artificial seawater. In the garage close to the aquarium, a 2000 litre PVC reservoir was placed and a special pump/valve-system was constructed which enabled the water to be pumped between the reservoir and the aquarium. When the rocks arrived we pumped about 1500 litres into the reservoir, placed the rocks and refilled the water. Later the reservoir was to be used for storing reserve water. Approximately 10% of the water is changed every year. There is also a special designed system for mixing artificial saltwater connected with the reservoir. Inside the reservoir their is a constant circulation and a weak aeration as well as a constant temperature of 22 ° C.

The decoration was fastened with plastic-strips like those used for bundling wires. We used an electric drill and other hardy methods for making a stable and harmonic decoration. It is most important to build a decoration that one is satisfied with and which is stable. If one continuously have to rebuild it and regroup the rocks, the small and rather tiny creatures will be harmed and one will prevent the "rock-biology" to develop. For this reason a careful planning and great care are needed.

We built the left side of the "cleft" very steep. The right side was moor sloped near the front, but very steep with an overhang near the back-window. We were lucky and found one single rock that had the perfect shape of a "reef-pillar". This rock was placed about 1/4 from the back window and a little to the right of the centreline. Later one it showed up to develop an almost perfect growth of algae consisting of brown Lobophora sp. and beautiful red, encrusting calcareous algae (possibly Neogoniolithon sp.). Until this day we have not placed any coral on the pillar, but let the growth of algae developed naturally.

The right, back corner of the decoration was ended about 30 cm in front of the back window leaving an open space between the decoration and the back-window. This part of the decoration did also reach the surface, which all together created an dramatic aesthetical effect. It looks like fish swim behind the decoration and into "the infinity". Just what we wanted ! It is also important to remember that many animals (especially the soft-corals) will grow very fast, and therefore a sufficient space above the decoration is needed.

Another factor to notice is the foremost part of the aquarium stretching about 50 cm into the living room. Here the decoration is not illuminated by the light from the HQI-lamps. Instead a single daylight light tube lights up this area. When fish swims in this part of the tank, they are weaker illuminated that those further back - an effect that strengthen the impression of depth. In this part of the aquarium we have placed animals that naturally live in weaker lights.

The bottom of the aquarium was covered with a 2-4 cm layer of fine coral sand mixed with some coral rubble.

The First Weeks

When decoration was completed and the aquarium was refilled with water, an exciting period began. Now it is most important to be patient ! Many tanks in Scandinavia have almost been ruined, or at least forced into a totally uncontrolled growth of filamentous algae, because of a too rapid introduction of too many animals.

As organics from the living stones were released, the concentration of nitrite and nitrate will normally increase rapidly. However, in our case nitrite did reach a maximum of only about 0.1 ppm and was zero after about two weeks. The concentration of nitrate was never measurable. We were happy and a bit surprised about this, but the major reasons that no nitrogen-compounds did build up were the combination of a heavy and very efficient skimming with high quality live rocks. As algae-nutrient was avoided we could only detect a minor blooming of diatomea followed by a minor growth of blue-greens and green thread algae that never became boring. If the stones had been of a lower quality (that is less fresh), as we often see with Singapore imports, we could have had a very different aquarium to deal with. During breakdown of organics, algae nutrients are produced, and it is normal to have some growth of filamentous algae during the first weeks and even months. If efficient skimming is not used, one must expect a much more intense growth due to a higher amount of organic being broken down in the aquarium.

Although we were lucky, it was important not to do hasty things at this point. The population of bacteria does need several weeks until it is stable and diverse enough to maintain a heavy populated aquarium. So even if things looked extremely good and there was no nitrogen-compounds to worry about, we knew that the aquarium was not yet ready for the input of several organisms. Nevertheless, as soon as the nitrite and nitrate reached zero, algae grazers and detritus feeders were introduced. We used six Zebrasoma flavescens , one Zebrasoma veliferum , a lot of brittle stars and some crawling sea cucumbers. A couple of soft corals were introduced to test the system, but apart from them we did not add any more animals until 12 weeks after completing the decorations.

The succession of algae was most pleasant. The brown and leafy Lobophora sp. and the more encrusting Dichtyota sp. started to grow during the first three weeks, and was soon followed by an intensive growth of the calcareous Neogoniolithon sp. Later on huge bushes of Halimeda opuntia showed an intense growth, and smaller populations of other Halimeda sp. did also appear. No blooming of the ugly red forms of blue-greens, which can be very boring, have occurred at any time. Until this day, nearly two years after the start and even when more than 100 fish and lot of invertebrates have been introduced, we have never felt that the growth of algae was not under control.

The Inhabitants

At present the aquarium contain a rich diversity of fish and invertebrates. The animals have mostly been added gradually one after another. However, the first invertebrates chosen was a group of large soft corals (mostly Sarcophyton and Sinularia sp.) - all bought from Germany. The majority of corals are soft corals, but the aquarium does also contain a number of stony corals that do very well. The most interesting result so far is undoubtedly the growth and prosperous development of two colonies of the Stolonifera Tubipora musica. This species is rarely offered for sale, which is good as it is most difficult to keep. Our specimens are both placed near the bottom in front of the pillar. Here they get a steady and rather strong current - and are doing excellent. There are a few Goniopora sp. and some colonies of the green Euphyllia ancora which are all marvellous. Some of the soft corals have in 20 months grown so much that they have nearly doubled their size, a feature that by no means is uncommon in a well maintained reef-aquarium.

The population of fish is dominated by 50 Chromis vidris . Among them are several small and colourful fish, but no large once. We have tried to avoid large fish as they produce a lot more waste products than the smaller once.

A project like this is of course very expensive and technicaly rather complicated. Even the best technique cannot work if it is not maintained. An important aspect is the clever and regular maintenance of lamps, skimmers, calcareous reactor, carbon filter and other units. Another aspect is the needed knowledge of the reef and animal biology to be able to maintain "a private reef". However, this aquarium stands as an example of what can be achieved if time, money, knowledge and great care are all combined.