OK I just have to speak up at this point about the debate between M/H lights and VHO for keeping clams or SPS corals. I'm using VHO and i'm a big fan of them, that being said I also have M/H lighting over parts of my tank "mostly for the shimmering effect". This tank is 30 inches deep and 150 gallons. The VHO's impart much better color over all and produce way less heat. I have 880 watts VHO and the growth of both derasa and crocea clams is great even without Ca reactor....derasa shell growth 1 inch of shell in 2.5 months and much better color and shell size in fluted area of crocea compaired to when I bought them. They are much larger than the size they were when I bought them. They are located near the top about a foot down. Maybe halides would allow for deeper placement but 30 inches is deep for a high light demand type of clam long term even with halides. I'm not saying one is better than the other but given enough wattage and correct spectrum either will work. And this was proven "Delbeek and Sprung".
And please spare me the arguements you Metal Halide guys as I also have 500 watts of 10,000 K german bulb for shimmering effect and better spectrum range used during peak lighting hours. I like them both but before I bought the halides growth was as mentioned above.
