For the most part they are a low maintenance addition to any tank, provided you have no problem maintaining consistent parameters.
I personally don't feed my clams anything. I used to grow and dose with phyto, and I've tried some mixtures produced for clams, but saw no difference. Feeding comes down size I think. Smaller clams do need additional food as they can't produce enough via photosynthesis, and filter feeding.
Clamsdirect.com is a great place to look for additional info. There is also a book by James Fatherree (
http://www.jlaquatics.com/phpstore/s...ct_ID=lit-clam) that is a nice easy intro to clams.
Any thoughts on what kind of clam you may want? Or are you just trying to get a feel if they are for you?