A couple of things need to be corrected here.
As others have said, the small clams will not need to be feed unless you run a very sterile tank as some people on RC do - Over skimmed, with ozone, etc..
Your clam can NOT live off of symbiotic photosythesis alone. There are nutrients they get from filter feeding that they need. Most reef tanks have enough phyto and other nutrients in their water to maintain a clam or clams.
Feeding your clam can not hurt it unless you do something wrong. Old decayed phyto full of anerobes for example would not be a good thing to bathe your clam in. Properly done regardless of what type of tank you maintain a feed clam will grow quicker and will be hardier. I chose not to feed because of the effort reward equation. My clams grow and survive fine without it. I am reasonably sure they would however grow faster if I feed them.
If someone loses a clam after feeding, this does not mean feeding killed the clam. If they feed the clam nasty decayed food again the proper conclusion is not that feeding is bad. Lastly, the fact that debate on the subject exists is not relevant unless someone presents a reasonable argument or properly controlled data.
- mark