T. gigas, T. derasa and T. Hippopus will usually do well under VHO's or PC's. In nature, T. gigas is found in deeper waters where pH, temperature, and salinity are extremely stable. It is therefore paramount that you aim to keep these parameters as stable as possible. H. hippopus are the least demanding of strong light and do well, in most tanks, under VHOs or PCs. In nature, T. derasa is found sitting on the sand bottom or coral rubble in relatively shallow and clear waters. As with most other clams, metal halides are recommened. However, there have been many successes from hobbyists keeping T. derasa under VHO or PC lighting in shallower tanks (less than 20" tall). Be aware that T. derasa is known for getting big in a short amount of time, usually around 20" in aquariums. It's a very quick grower.
All of the clams I listed grow large and will grow fast. They often need large sized aquariums. T. Squamosa, T. Crocea, and T. Maxima usually do best under halides, although many have successfully kept T. Squamosa under PC's or VHO's with limited success. T. Squamosa is also a fast grower.
Take Care,
Graham
