Building a Reef Aquarium Part 4

In my last article I covered the installation of the live rock into the aquarium and the maturation of the system, in this article I will cover the stocking of corals and the considerations that go with selecting the species and their positioning within the aquarium.

Performance of the system so far
Well everything is working very well, I have not had any problems with any of the equipment and everything has been trouble free. The new V2 calcium reactor and monitoring equipment that I have tried out is performing well as are the Seio superflow pumps which I have not used before. Since the end of the maturation cycle of the uncured live rock the water parameters have been very good and are now stable at the following readings:

Salinity 33ppt Temperature: 26-27C Ammonia: 0.0ppm Nitrite: 0.0ppm Nitrate: 0.0ppm Phosphate: 0.00ppm Magnesium: 1440ppm

You may remember from my last article that there was a flourishing growth of Sargassum macro algae coming from the live rock that the grazers in the tank so far (Yellow Tang, Dove snails and Turbo snails) would not feed on. To combat this I have added a Unicorn Tang (Naso unicornis) which is around six inches in length. These Tangs do grow very large (almost 24″ in the wild) however I am hoping that due to being kept in an aquarium it will not grow anywhere near that big, should this prove not to be the case then it will be donated to a larger aquarium once it outgrows this one.
The Yellow Tang had already been living in the system on it’s own for several weeks before I added the Unicorn Tang and at first it took great objection to the introduction of this new fish. There was quite a bit of fighting between the two which resulted in several cuts on the Unicorn Tang imposed by the Yellow Tangs larger scalpels. I was a little concerned abut these cuts at first due to their severity but they healed up within a couple of days and after five days of being in the same system the fighting stopped. Even though there was plenty of scrapping going on at first this did not stop the Unicorn tang getting stuck straight into the population of Sargassum and within a week and a half it had completely removed the rather hearty distribution of this macro algae.
There is a little green algae remaining on some areas of the sand bed but all of the rockwork is now free of any macro or filamentous algae. There is however a copious growth of various species of coraline algae, this is not a problem on the rockwork or glass of the aquarium but there are abundant amounts of branching coraline algae, probably a Jania species (fig 1) that are growing on the substrate. Although these are quite pretty and an indication of good water quality they are spoiling the nice white sand effect that I want to achieve. However without dropping the water quality there is not a lot I can do about it so for the time being I will just have to wait and see what happens.

Stocking the Corals
People often ask me how quickly can they start to stock their tank with corals and how many can they add at once. You can start adding corals as soon as your water quality is good enough, if you have set up a Berlin style system and used cured live rock so that there are no ammonia, nitrite or nitrate spikes then there is really no reason why you cannot start adding corals almost straight away. However, new aquarists should be wary, there are many things to learn when keeping a reef aquarium and it helps to become familiar with your system, learning how to keep things stable, performing water changes correctly, water testing, etc. But provided that your water chemistry is good and you know what you are doing there is no reason why you should not start stocking corals straight away.
The other question is how many corals can I add at once? Corals are different to fish in that they do not produce nitrogenous waste in the same way that fish do and so there is not the problem of having to let the levels of bacteria in your filtration media build up to deal with the additional ammonia produced by each new fish added. For this reason it is possible to add many corals at the same time, however just because you can do this does not mean that you should! Corals are expensive and there are many things that can go wrong with a system whether you are an experienced reefkeeper or a novice and the last thing that you want to do is spend all your hard earned cash on stocking your system with corals all at once only for there to be some unforseen problem and numerous fatalities.
Corals are a great indicator of the conditions in your aquarium and they will soon let you know if they are not happy with something by their appearance, but it takes time to learn how to identify reactions in corals so if you are a novice it is best to start with hardy species of coral, see how they do and then slowly build up your stocking density as you gain experience. My situation is slightly different in that I run a commercial coral farm and so have a wide range of back-up systems should there be a problem with this tank. I am also stocking the aquarium almost exclusively with corals taken from my other systems and have had some of these corals for nearly ten years so I am very familiar with them and know what to look out for should they have any health problems. So with that being the situation over a period of two to three weeks I added over a hundred frags and small colonies of coral to the tank.

Light requirements
Two of the key factors when placing corals within your aquarium are water flow and light intensity. The light intensity within your aquarium will vary massively from position to position, particularly if you are using metal halides, even if you are using flourescent tubes the variation in light intensity according to depth will be very significant, you will also find that flousecent tubes produce significantly more light towards the centre of the tubes than at either end. With this in mind I took a number of light readings throughout the aquarium with a quantum meter, the results are shown in the diagram in figure 2.

In this instance the distance from the surface of the water to the halide lamps (not the cover glass) was 13cm and the distance from the water surface to the T5 tubes was 4cm The readings given in the diagram were taken at the surface of the rock at each position and you can see that the intensity of light varies greatly throughout the aquarium. The lighting in the aquarium consists of two 250w 10,000Kelvin BLV double ended metal halides lamps, two 54w T5 white tubes and two 54w T5 blue tubes. With the information provided by the light meter I was able to choose where to position each species of coral according to it’s preferred light requirements. It is worth noting that these readings were taken at the surface of the rock and as the corals grow the light intensity that they receive will increase quite significantly as many of them grow upwards towards the light source.
Either end of the aquarium were the areas that had the lowest light intensities, and the left-hand end also had slower water movement so for these areas I had to choose corals suitable to these conditions. On the left hand side I positioned Alveopora, Euphyllia paradivisa and Montipora capitata, all of which prefer lower light intensities. On the right-hand side I positioned Anthelia, Seriatopora gutattus and a green Stylophora pistillata. Although the Stylophora can tolerate a range of light intensities, this particular one has better green colouration and growth rates under lower light intensities. The rest of the aquarium was planted with a mix of SPS frags and small colonies as well as a few species of LPS and soft corals.
Table 1. Coral species within aquarium and their relevant positions shown in fig 3.

When you choose your corals it is important to do as much research about their requirements as you can, particularly preferred light intensities. There is information out there now about the amount of light that different species of coral like, and even if you don’t have a light meter then a little research on the web will provide you with more information on the way that light is distributed through an aquarium from different light sources. As you can see from figure 3 the species that are known to prefer high light intensities have been given the brightest spots within the aquarium, particularly the Acropora species, whereas those that can be found commonly in deeper areas of coral reefs have been given more subdued lighting positions.
It is also important when you are positioning your corals to take into account growth, some species of coral will grow very rapidly whereas other species can be rather slow. Always position plating species lower down in the aquarium as these often grow quickly and will shade out any areas below them. Also by positioning these flatter species lower down and towards the front of the aquarium and taller branching species towards the back then you will increase the illusion of depth within the tank. When you buy corals from an aquarium shop they may well have been under conditions of low light intensity for several weeks so it is important not to cause them stress by suddenly exposing them to much higher light intensities than they have become accustomed. Always check how long a coral has been in a shop for and pay attention to the lighting that it is under, check the wattage and kelvin rating of the shops lamps and also the distance that the coral has been kept from the source of light. Remember as you go from 10,000 kelvin to 14,000 kelvin to 20,000 kelvin lamps the amount of light that they emit drops by around 25-30% with each increase in Kelvin rating for lamps of the same wattage. If you think that the final position that you want for a coral in your aquarium is much brighter than the light intensities that it has been kept under for the previous few weeks then you are best starting your coral off lower down in your aquarium and then gradually moving it up over a period of a couple of weeks until it is in it’s final position.
Within aquaria most corals seem to be able to tolerate a sudden increase in light intensity of 100µE/m²/sec without the coral having to result to bleaching, some species particularly the  intense light loving species such as Acroporas and some Montiporas can tolerate a sudden increase of around 200µE/m²/sec without causing them too much stress but be particularly careful with many species of LPS coral and deeper water corals as their tolerance to higher light intensities and sudden increases in light is much less than that for most species of shallow water SPS coral.
The bleaching event that you see in corals, particularly in aquaria under circumstances where a coral has suddenly been exposed to a much higher intensity of light is actually a safety mechanism of the coral itself. One of the results of a sudden increase in the amount of light that a coral is exposed to is an increase in the rate of photosynthesis and an increase in photosynthetic products. One of the products of photosynthesis is oxygen, in certain forms oxygen combining with water can form hydrogen peroxide which is harmful to living tissues, the coral does produce an enzyme to combat this hydrogen peroxide by-product but if there is a sudden increase in photosynthesis then the coral may not be able to cope with the additional oxygen and hydrogen peroxide produced and so the zooxanthellae are expelled. These bleaching events may be slight or a high percentage of the zooxanthellae may be expelled but they are never total and some zooxanthellae always remain so the coral can recover.
When you are positioning your corals look for paling on the upper surfaces of the coral as an indication of partial bleaching and if you see this then move your coral to a lower light intensity position. Once the final position for your coral has been established it is vital to fix the coral securely in place to prevent it moving or tumbling down and damaging other corals and itself. Aquascaping putty is the most common and easy way of securely fixing your corals in place.

Feeding your corals
Now that the corals are in place it is beneficial to start feeding them. Zooxanthellae require nitrogenous compounds to enable photosynthesis to occur, in most systems were there is a healthy stocking of fish the corals are able to gain nutrition from both the waste products of the fish as well as nutrients released into the water from the foods that the fish are provided with. However, in systems that have a very high stocking density of corals or a low stocking density of fish, nitrogenous compounds may be in short supply and hence zooxanthellae can starve.
Corals will feed on plankton from the water and pass on metabolic waste products to the zooxanthellae to enable photosynthesis to occur and the coral is able to regulate the amount of waste products that it passes on to the zooxanthellae to control the amount of photosynthesis. The ideal way of maintaining the delicate balance between the coral and it’s zooxanthellae is by providing a low nutrient environment (although not below natural reef water levels which can be achieved in certain systems) and a good supply of plankton for the coral to feed on. In this way you are leaving the coral the ability to regulate the amount of nutrients that are passed onto the zooxanthellae from metabolic waste products and hence regulate the rate of photosynthesis that it needs.
So what do you feed your corals? Well there is no simple answer to that as different corals will feed on many different things. Some of the larger LPS corals will feed on larger pieces of shrimp or even small fish, soft corals vary massively from fine plankton feeders to larger predating species. Most SPS corals will feed on various types of plankton. It is important to asses your individual corals dietary needs and feed them accordingly. Generally I use a mix of different things to feed various groups of corals, one of the simplest ways of feeding a great variety of corals is by the use of phytoplankton. Phytoplankton is at the bottom of the food chain on coral reefs and many species of coral will feed directly on phytoplankton, also by feeding phytoplankton to your system you are providing a food source for larger species of zooplankton to feed on and the population size of these zooplankton within your aquarium will increase. Most species of coral will feed on various types of zooplankton growing in your system. Try to use a good quality live phytoplankton, I personally use Live Phytofeast which is a blend of five different species of phytoplankton which I have now started adding to the aquarium on a daily basis. I also feed my corals a mix of live zooplankton which are cultured separately, namely rotifers and copepods and these are added to the system two or three times a week. For the larger LPS corals and some of the mushrooms I feed dead Brine shrimp directly to the corals a couple of times a week. There are numerous other types of coral food on the market that you may want to try but be careful of overfeeding dead plankton types as this may deteriorate water quality if used in excess.
The difference in health and growth rates of corals if fed well is substantial, the best rule of thumb that I have found for feeding corals is to give them as much food as you can without deteriorating the water quality.
Most of the corals have now been added to the system, there are still a few places that I have left for new species but for the most part the coral stocking is complete, we will come back and take a look at the system again in about 6 months time to see how they have progressed. The final stage of the build of this aquarium is approaching and in the next article I will cover the stocking of the fish.