Coelenterates must of course present all the necessary signs of good health before being introduced to an aquarium: they should be unfurled, swollen, and full of water. If they are in a bad state, they look wilted and may not be viable. Anthozoa like clear and well-lit water, as it benefits both them and the Zooxanthel-lae to which they play host. They must be placed close to the surface of the aquarium. The water quality is, of course, very important, and in addition the calcium
WHAT IF YOU TOUCH A COELENTERATE?
Some species have a greater stinging capability than others. Serious reactions, such as cramps or breathing difficulties, rarely encountered among aquarists, can be provoked by certain medusas (jellyfish), due to a phenomenon known as anaphylaxis: the body is sensitized to the venom after an initial contact and becomes more vulnerable. In the event of an accident, detach the tentacles and, above all, do not rub your eyes. Treat the stung area immediately with diluted ammonia, but it is best to consult a doctor.
levels must be monitored with particularly close attention.
The skeleton of corals is mainly composed of calcium carbonate, which is abundant in the natural habitat - up to 500 mg/liter - and so an aquarium that is to be inhabited by corals must also have the same level.
The concentration in an aquarium can sometimes fall below 300 mg/liter, depending on how many organisms there are in the tank, and in these cases calcium must be added. Several relatively simple methods for raising the calcium level are detailed in the box on page 173.
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