Reefrunner262,
You will probably get a lot of different opinions on this subject. Here is what I think. VHO and Power Compact can be done,. but 150 watts of vho are not enough. Croceas, Maximas are the most light intense seeking clams there are. I have kept both under power compact lighting, but it was still 400 watts of light. I do reccomend Metal Halide lighting. In my holding tanks I use 175 watt 10 k metal halides. The clams are only about 6 inches under water, and lights are suspended about 10 inches above water, so the lights are close.
In my personal tank I use 400 watt halides. In my opinion you need more lighting than what you have. I do not belive in the watt per gallon rule. But 175, or 250 watt halides would give your clams what they need. Also when ordering your clams, try to get 3 inch or larger clams, as they have developed the need Zooxanthallae to process what they need to live and grow from our lighting. Smaller clams are not quite fully photosynthetic, and should be fed a good live food like DT's phytoplankton.
Feel free to email me if you have more questions.
Rob