this is an interesting excerpt from
The Reef Aqarium - Sprung & Delbeek - Volume II Page 313 - 316

It might answer the question why zoanthids develop diseases in tanks.

Here are the important highlights.

Lighting:

Strong illumination, particularly if it has a high quantity of UV wavelength, stimulates the production (via photosynthesis by zooxanthellae) of toxic high levels of oxygen in the tissue of the host anemone, corallimorpharian, or coral. We should clarify that the molecular oxygen produced is not so problematic. When the anemone is illuminated by high intensity light, the energetic UV wavelengths in the presense of photosynthesitizing agents such as chlorophyll and flavins act synergistically to produce singlet oxyen and the superoxide radical (02), which is very reactive and readily forms hydrogen peroxide H202 (Shick, 1991). If you've ever poured hydrogen peroxide on a cut or put it in your hair you know it is also very reactive, and not something you want accumulating in your tissues! Dyken and Shick (1982) describe the enzymatic defenses utilized to counter the effects of the superoxide. In one strategy the enzyme superoxide dismutase keeps cellular levels of superoxide low while other enzymes, catalase and peroxidase, convert the hydrogen peroxide produced into water and oxygen. Other biochemical antioxidants may also be used instead of enzymes (Tapley, Shick and Smith, 1988). Dykens (1984) showed that zooxanthellae have high levels of superoxide dismutase activity, and enzyme used is a form with copper and zinc ions, a form not known from other unicellular eukaryotic algae.

What is mysterious is the effect of trace elements on this condition. Iodine (aspotassium iodide) seems to help prevent this problem, and it is possible that other trace elements help also.
Perhaps the trace quantities of copper and zinc from added weekly suppliments assist in the formation of the zooxanthellae's special enzymes. Prehaps there is an antioxidant effect achieved by the iodide being converted to iodate, as suggested by Buddemeier in Delbeek and Sprung (1994). With all the talk about antioxidants and health lately, it's no wonder this has application to the subject of reef corals, anemones, ect.

---------------------------------------------------------

For most photosynthetic cnidarians adaptation to the artificial light is just a matter of time, and it involves changes in pigment density and quantity of zooxanthellae. for some the adaptation is difficult, and ifthey are daily stressed by light intensity that produces toxic oxygen radicals beyond their physiological cpacity to detoxify them, they may never adapt. the light in nature is pulsed because of the passage of clouds. the periods of rest provided do actually assist in preventing the accumulation of superoxide by limiting it's production. It is not essential to duplicate this pulsing of the light, but it is possible to do it (Gutierrez, 1991).


here's the link i found it:
http://www.reefcentral.com/forums/sh...5&pagenumber=2