I have to disagree with MiNd and xtremereefer here. T. derasa come from very clearwater, low turbidity, lagoonal areas where they receive strong sunlight all day long. Although found in moderate depths, the water is so clear and waters are calmer due to barrier protection. To quote Daniel Knop "T. derasa seems to do best when kept under 250- or 400-watt metal halide lamps". T. derasa that do not receive strong lighting will soon show signs of color loss. When purchasing a T. derasa, color plays a major role in the selection process. Clams acclimate alot more slowly to lighting changes than do corals and some may never regain their colors once they are lost.
Additionally, T. derasa are very rarely found on rocks.. they grow down on the substrate amongst rubble. Therefore, moving them up onto the rockwork to get them closer to the light will not make for a very natural habitat for them.
- JT