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Live Coral

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Friday, January 11, 2008


The hierarchy of difficulty in aquaria is as follows: cold freshwater, tropical freshwater, saltwater, live planted freshwater, live coral saltwater. Cold freshwater aquaria, which are most often goldfish tanks, are the easiest to maintain while the live coral saltwater aquarium is the most difficult. What makes live coral so hard to maintain? Water quality! Live coral need very specific conditions in order to stay alive which includes the right nutrients in the water, the right lighting, the right temperature the right pH etc. Maintaining the proper conditions for a coral reef aquarium is time consuming and most of all, it is expensive! A basic lighting system for a small coral reef aquarium costs in excess of $500. Most people can’t even fathom spending that much money on lights. This is the primary reason why I have not been able to keep live coral at home….yet…

The most important thing live corals need is light. Metal halide lights are the most common lighting solution because not only do they produce light in the right wavelength, but also the right intensity. In short, metal halide lights replicate the kind of tropical sunshine live corals receive in the wild. However, metal halides take a long time to reach their full intensity because they produce light by heating a filament to a plasma state. As you can imagine, this takes some time so until the metal halides reach their full intensity, actinic fluorescent lights that emit blue light are used to illuminate the corals. The lights are on a 12 hours cycle where they turn on during the daytime and turn off at night to simulate the natural cycle of the sun. Let me back up for a moment. Corals are photosynthetic organisms. That is to say, they derive their nutrition from taking in sunlight and synthesizing their own food the way plants do. However, corals are not plants. They are animals. Corals photosynthesize with the help of zooxanthellae, tiny algae that lives within the tissues of the coral. The zooxanthellae produce food for the coral and in exchange, the coral gives the zooxanthellae a place to live. If the zooxanthellae do not receive enough illumination to photosynthesize, the coral starves. The corals themselves can also capture food that floats by but their primary source of nutrition is food from the zooxanthellae. Corals can also catch plankton as a secondary means obtaining nutrition.

Next, the corals need calcium to build their skeletons and keep them strong, kinda like humans! Except, you cannot give a coral a cup of milk. Instead, calcium hydroxide is added to the aquarium water by means of a bucket slowly dripping calcium hydroxide solution into the overflow box of the exhibit. This allows the calcium to fully dissolve into the water so that the corals can absorb it. Calcium hydroxide is added to the exhibit twice daily. Additionally, strontium chloride is added to the water to help with building strong bones for the corals but this is not added as often as the calcium.

Next, lugol is added to the water to combat jelly disease. In their natural environment as well as in the aquarium, corals face great competition for space. The coral reef is very crowded and real estate is hard to find. Therefore, other organisms such as protozoans will often hurt the coral in order to get their turf. The protozoans will grow over the corals, the protozoans on top of the coral thereby that section of coral appear jelly-like. Adding lugol helps keep the protozoans from gaining too much ground but it also encourages algae growth. Like the protozoans, algae can also crowd out the coral Therefore, as far as lugols are concerned, it is a constant battle to determine exactly how much must be added to fight jelly disease as well as prevent algae growth.

The pH of the water must be kept constant. On the wall, next to the sump is a controller that monitors the pH of the water. If it ever becomes too low, the aragonite inside a calcium reactor will be forced to dissolve and re-stabilize it.

Water quality is checked by the laboratory team at the Aquarium. The technicians take water samples from the exhibit and measure the water parameters for everything from ammonia to chloroforms. This is very important in coral husbandry. Any change or insufficiency in the water quality can cause the corals to turn white, a.k.a. bleaching, which means death for the coral. At the Aquarium, trace elements are tested via gas spectrometer. For the home hobbyist, it is a never ending battle that must be fought with little water quality test kits.

Lastly, coral maintenance also includes trimming back the corals. Again, corals are animals. Animals can act territorial and fight for space. Coral also fight with the use of their nematocyst tipped tentacles. Coral tentacles looks like clear strings of spaghetti that can sting you. By trimming back the corals, we can ensure that the corals don’t fight. This is accomplished with a hammer and chisel because coral skeleton is very difficult to cut through. The fragments obtained from each trimming are taken upstairs to the coral propagation table where the ‘frags’ await their fate of either going to another aquarium or being sold to reputable wholesalers.

While Amy showed me how coral maintenance is done, she let me help out by cleaning the filter socks. These socks were originally hanging off the overflow boxes so that they could catch any debris coming out of the aquarium. I managed to squeeze a lot of stuff out of the socks which just shows you how much waste corals can produce.

Well, that is all. I’d like to thank Amy, the hardcore coral reefer for showing me how coral maintenance is done. Thanks!

Live Coral
Multiple metal halide pendants illuminate this exhibit. These lights generate tremendously intense illumination as well as a lot of heat.  | © David Chen
Live Coral
Calcium hydroxide must be added to the water daily.  | © David Chen
Live Coral
To prevent the corals from overgrowing each other and fighting, they have to be trimmed. To do this, the task requires the use of a hammer and chisel.  | © David Chen
Live Coral
Look at how much waste I wrung out of just one filter bag.  | © David Chen

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MarineDepot's avatar


Monday, January 14, 2008 10:52 AM

Very informative post. More like this would be great! Some home aquarists use Lugols, too ... I know I did.

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Thursday, January 17, 2008 07:23 PM

I haven’t heard of many aquarists or aquariums using lugols as a preventative directly dosed to the tank.  I’ve heard of it for dips and such.  Any more info on it’s use as a preventative like this?

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Monday, January 21, 2008 11:23 AM

As far as adding it straight to the tank, you add a one drop weekly for every 25 gallons into an area of high water flow. You can also dilute it in one cup of aquarium water and administer directly over xenia colonies or soft corals with rigid tubing or a pipette.

All blogs and comments represent the views of the individual authors and not necessarily those of the Aquarium.

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