Throughout December and January, we have been very busy refurbishing our large marine aquarium (dimensions: 3.3m x 1.04m x 0.9m, totalling approximately 3 cubic metres (108 cubic feet).

In aquariology, there is a “Fish only” [FO] aquarium and “Reef” aquarium [R] whereas we were developing the more complex “Fish-only with live rocks” aquarium [FOWLR]. This latter type is designed to showcase fish along with living corals naturally colonised by a variety of marine life (sponges, invertebrates, beneficial nitrifying bacteria). This creates a natural-looking environment and provides excellent supplemental filtration to help maintain a stable eco-system. Usually, a FOWLR aquarium does not contain living corals or invertebrates as these may get eaten by the fish, so to prevent this we will be feeding the occupants daily with a variety of foods.

Project Priorities

  • Create a safe environment for marine life, staff and visitors;
  • avoid stagnant water and sedimentation areas; easy to clean and to keep clean; hide pipes and pumps;
  • representative of Maldivian waters.

Options – materials for the aquarium background

  • Expanded polystyrene (inexpensive, but artificial in appearance and not durable);
  • prompt natural cement [PNC] (porous, lightweight and easy to model, but not available in Maldives);
  • grid with stones (natural elements, but heavy and bulky installation with sedimentation areas);
  • polyurethane foam (natural in appearance, durable and lightweight, but expensive and potentially toxic).

From these potentials materials, we choose to make the background with “polyurethane foam”, which is commonly used in public aquaria (as well as in home furniture). This foam is made from two separate ingredients that harden when mixed together and allowed to dry. Before drying, the foam can be modelled and shaped to cover the walls, hide technical equipment and give a natural appearance. Whilst modelling, we were careful to keep the thickness of the foam to a minimum (<10cm) to allow the maximum space for the fish to swim around. Finally, to neutralise any potential toxicity of the foam, we applied four coats of “Epoxy resin”, commonly used in marine aquaria for waterproofing.

Basic schematic showing aquarium dimensions

Carla and Aku hard at work

The live-rocks were taken from different places of our house reef, and we mainly chose dead coral plates and porous stones. We drilled the coral plates and supported them around a central PVC pipe acting as a supportive column.

300kg of sand was taken directly from the sea to keep its biological benefits. We then added soft and hard varieties of living corals, along with anemones and other marine life beneficial to the ecosystem. We chose different species of corals, sponges and ascidians, to represent Maldivian biodiversity. Crustaceans, echinoderms and molluscs were also added, to facilitate in the tank cleaning process and help to create a balanced and stable ecosystem.

The fish population was carefully selected according to temperament, ability to live together and biological function in the food chain. We avoided carnivorous predators and chose smaller sized fish – a mixture of filter-feeders, detritivores, herbivores and omnivores. Once the fish were caught, we acclimatised them in our turtle pool to become accustomed to dry foods and a closed environment. Aggressive fish and those which did not acclimatise well were returned back to the sea. (As a bonus, having fish in the turtle pools was also beneficial for our rehabilitation turtle residents, as they keep algal growth under control and remove parasites from the turtles).

Slideshow – refurbishment of our new marine aquarium

The Construction and Refurbishment Process

The Inhabitants


Sample of fish caught
(left, click to enlarge)
Maori wrasse (* top), Picasso triggerfish (left),
Brown butterflyfish (middle), cleaner wrasse (left-middle),
Regal angelfish (right), Emperor angelfish (bottom),
Honeycomb grouper (* bottom right).
(*) The grouper and the Maori wrasse were released due to their size and predator function.

STONY CORALS
Acropora species, Cap-like mushroom coral (Halomitra pileus), Porites species, Artistic coral (Platygyra daedalea).
– Green Pavona (Pavona maldiviensis), Angular coral (Favites halicora), Sun coral (Diploastrea helipora), Flower-pot coral (Goniopora species).

SOFT CORALS
– Bubble coral pearl (Physogyra species), Blue coral (Heliopora coerulea), Mushroom leather coral (Sacrophyton species), Long-lobed cladiella (Cladiella species).

INVERTEBRATES
– Sea anemone (Heteractis magnifica), Sponge (Acabthella klethra), Red pencil urchin (Phyllacanthus imperialis), Mathae’s sea urchin (Echinometra mathae).
– Sea star (Choriaster granulatus), Giant clam (Tridacna squamosa), Sea cucumber (Isostichopus badionotus), hermit crab (Dardanus lagapodes).

VERTEBRATES (FISH)
– Picasso triggerfish (Rhinecanthus aculeatus), Blotched porcupinefish (Diodon liturosus), Crescent perch (Terapon jarbua), Emperor angelfish (Pomacanthus imperator).
– Blue-streak cleaner wrasse (Labroides dimidiatus), Maldivian cardinal fish (Apogon maldivienses), Saddled pufferfish (Canthigaster valentini), Brown tang (Zebrasoma scopas).

Updates February 2017

On 12 February, we upgraded our pumps to more powerful models, so now the tank volume is renewed every 1.5 hours, giving us a better supply of oxygenated water. We also introduced some new inhabitants this month:

  • White-spotted pufferfish (Canthigaster janthinoptera)
  • Adorned wrasse (Biochoeres cosmetus)
  • Six-spots sleeper-goby (Valencienna sexguttata)
  • Bird wrasse (Gomphosus caeruleus)
  • Imposter blenny (Plagiotremus phenax)
  • Monocle bream (Scolopsis bilineata)
  • Eye-line surgeonfish (Acanthurus nigricauda)
  • Crested sabretooth blenny (Petroscirtes mitratus)

The water parameters are checked daily, and remain safely within the range for the health of our aquarium inhabitants.

One of the current challenges down in our Fish Lab is maintaining the healthy marine life in our newly renovated aquarium, until conditions have matured and stabilised. The corals in particular require specific water and sunlight conditions, and they are sensitive to pollution, sediments and any water changes. We hold 11 species of hard coral and 4 species of soft corals, and we have been taking photographs every 10 days to assess their health over time. We feed daily with 1L Artemia brine shrimp and have increased the light intensity to encourage photosynthesis by their zooxanthellae. Overall, the hard coral family has shown the best health (e.g.: Diploastrea heliopora, Favites halicora) whereas the soft corals are not faring as well, especially species of Cladiella and Sacrophyton.

Updates March 2017

Throughout March, the coral life in our aquarium remained stable, except for Acropora and Pocillopora species which showed some bleaching. Using a stronger light to increase the activity of their zooxanthellae (which provide 90% of their energy) did not help, so we chose to transplant them onto our coral frames out in the lagoon. The soft corals which were the most affected in January and February have now recovered.

In aquariology there are 3 different filtering methods:

  • Mechanical Filtration (foam, sand, bag): the first step, trapping organic matter particles suspended in the water avoids sedimentation in the tank [we use: 4 sand filters (10μm) followed by 4 ultrafiltration filter bags (5 μm)].
  • Biological Filtration (ceramic, bio-balls, living stones): bacterial action transforms dissolved organic matter to cycle Nitrogen [we use: living stones inside the tank].
  • Chemical Filtration (charcoal, zeolite, ultraviolet): to modify the chemical parameters of water. Activated charcoal removes organic dyes; ‘green’ water is sterilised with UV [we use: a UV filter].

In order to maintain good water quality in the aquarium, we perform regular cleaning tasks ranging from daily backwashing to annual sand filter cleaning. During March, we cleaned 2 of the 4 sand filters. Each filter contains 450kg of sand, and it took 2 full days of hard work to clean all of the sand from just one filter. We also discovered that some fish had made a home in the filters! (The two puffer fish were moved to our aquarium).

Aquarium – new arrivals

  • Long-nose filefish (Oxymonacanthus longirostris)
  • Yellow-tail basslet (Pseudanthias evansi)
  • Two-colour cleaner wrasse (Labroides bicolor)
  • Turn-worm blenny (Plagiotremus rhinorhynchos)
  • Two-colour combtooth blenny (Ecsenius bicolor)
  • Lined soapfish (Grammistes sexlineatus)
  • Red fire-goby (Nemateleotris magnifica)
  • Yellow-head butterflyfish (Chaetodon xanthocephalus)
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