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Where to position corals within the Aquarium

Date Published - 29th October 2012 - Published by - iQuatics Ltd

So you’ve just got your hands on a new coral and your about to acclimatise it and put it into your aquarium. Do you know where best to put the coral or what its light dependency levels are? In this article we will try to help you understand why coral placement is more important than just placing the corals where they look attractive.

As you will know there are 100’s of different species of coral, all of which will have individual lighting requirements, some will need strong lighting others will not like lighting at all, this is the reason it is important to research your corals before you buy them, try and steer clear of impulse buys as these can prove costly in the long run.
One of the first things to consider with your new coral is its lighting requirements, does it need intense lighting or is it less light dependent and can be placed lower down in the aquarium? The key to making this decision is research; try to look at several different sources when doing research, especially if using the internet. Because the internet is accessible to everyone there is a lot of misinformation out there, this is why looking at one website or article is risky as the one you read could be wrong, by reading several different articles you will be able to make your own decisions based on all of the information you have read.
When placing a coral it is important you consider its lighting requirement’s before you place it in its location, this is due to the fact that once a coral has adapted to life in its new location moving it even a small distance will force the coral to re-adapt. This re-adaption process can take weeks and each time it occurs the coral will show signs of stress and inhabited growth.
There are now many different types of lighting available to aquarists below are some of the most common and widely used.

Fluorescent lighting

This method of lighting is still the most popular for reef keepers, especially those that keep Softies and LPS (Large Polyped Stony) corals. Fortunately huge strides have been made in this type of lighting and the introduction of T5 high output tubes has allowed reef keepers to make strides forward in the corals they are now able to keep in there aquariums. Also with the addition of specially designed lighting units that allow several tubes to be run at once it is now possible for SPS (Small Polyped Stoney) corals to be kept under T5 lighting, as long as placement is considered thoroughly.

Metal halide lighting

Metal halide lighting is the closest source of light we have that replicates the sun; it is a high intensity source of light that is emitted from a single point, very much like the sun itself. Using a metal halide light above your aquarium will allow you to keep most corals with ease, but it is also worth considering that a halide may be too intense for some corals.

L.E.D Lighting

The new kid on the block! LED lighting is still a new concept when it comes to using them above a reef tank and although great strides are being made in the technology they are still regarded by most as being unable to sustain a reef tank solely. Many people who are using LED lighting are also using T5’s as a supplementary form of lighting. As with the halide LED’s are a focused source of light that uses lenses to direct the light. If you are considering using LED’S above your reef tank it is important that you thoroughly look into the spectrum’s emitted and ensure that they will enable the zooxanthellae within the corals to photosynthesize. Without the ability to photosynthesis your coral will not flourish in the aquarium!


Now we move onto a subject that is vastly overlooked in reef aquaria, as technologies and understanding have advanced our ability to keep thriving coral reefs in our tanks has become much easier. This has also meant that more and more corals are becoming available to us and we are growing corals to bigger sizes than we have managed over the last 10-20 years.  This means that as corals grow they are coming into closer proximity to each other than they have done in home aquaria.
Corals have developed several specialized mechanisms for protection and competition with other corals. These include sweeper tentacles, mesenterial filaments, and terpenoid compounds.

Sweeper Tentacles

Sweeper tentacles are the most common defense mechanisms in the hard corals, and also occur in some soft corals. Specialized stinging cells called ‘nematocysts’ are existent in these tentacles and can attack a rival coral and literally “burn” it to the point of either killing it or severely damaging it. The length of these sweeper tentacles is not related to the length of the normal coral polyp and may be many times longer.

Mesenterial Filaments

In addition to sweeper tentacles, several hard coral species can produce mesenterial filaments from their stomachs. Corals such as Favia and Scolymia have this capacity.These filaments can kill or devour other coral polyps through a process similar to digestion. Some corals even have the capacity to produce both sweeper tentacles and mesenterial filaments, enabling them to fight with other corals all around them

Terpenoid Compounds

The soft corals generally compete with the hard corals by releasing ‘terpenoid’ or ‘sarcophine’ compounds into the water to injure or impede the growth of a neighbouring coral, and then overgrow these inhibited corals in a process called “allelopathy” Like their name implies, these compounds are similar to turpentine in chemical structure and in most instances, are just as toxic. By releasing these compounds, the soft coral injures these neighbouring stony corals and can then grow above them, eventually blocking out the light that they are both dependent which can kill the harder coral.


While our home aquaria may not contain the abundance of life that an actual reef does, care should still be taken to try and minimize the amount of aggression amongst your corals. This can be done by ensuring that each coral has adequate space to grow without coming into contact with another coral.
The rule of thumb for coral spacing is just that, a guideline the only person who will know if the corals are too close to each other is you and therefore it is important that you understand your own aquarium thoroughly.
Hard Corals (SPS & LPS)
LPS corals should have around 15cm in all directions as it is not uncommon for sweeper tentacles to be this long. For SPS corals the zone is slightly less of around 5-8cm however it should be considered that SPS corals are the fastest growing of all the corals so extra space should be allowed for their growth
Soft Corals
The space between soft corals does not need to be as big as soft corals do not burn each other to the same degree that hard corals do. However it is important to consider a faster growing soft coral can overshadow a slower one and eventually starve it of its light source. They should also be positioned so there terpenoids do not come into contact with their neighbours

Minimize tip over potential

Tip over potential is the likelihood that one coral will tip over and land on another coral and as a result burn or be burnt by another coral. The burned area can quickly become infected and as a result the whole colony dies.

Water movement

The final thing to consider when placing your coral is water movement, most corals do not have the ability to clean themselves and rely on strong water movement to perform this task for them.  If water movement around the corals are insufficient detritus will settle on the corals and decay which can quickly lead to the demise of the coral, however not all coral need the same amount of water movement.

Strong current corals

These are corals that do best with strong water movement; these corals usually have small polyps and are large or encrusting type corals. Corals such as Acropora and Turbinaria all fall into this category, these corals can take the strongest water movement in a reef tank.

Moderate current corals

The next group of corals require a more moderate current as they come from lagoons and back reefs where the current is not so strong. Most of these corals have either large polyps or are large polyped encrusting corals. Corals such as Star Polyps,Goniopora and leather corals fall into this category.

Low current corals

This group still requires water movement, but it is only a small amount relative to the other groups. This group includes mushrooms and bubble corals.
You have just read another great aquarium blog post by iQuatics. If you would like us to blog about a specific subject or have your own aquarium blog content you would like published on our website, please get in touch. Together we can help grow the iQuatics aquarium blog into a vast resource full of combined industry knowledge.

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