You really need to understand the needs of animals BEFORE you buy them.
The answer is that your clam MIGHT be alright, but might NOT, depending on how much lighting you have, and where it is placed. Croceas have the highest lighting requirements of all the Tradacnids, and IMO, it was a mistake for you to buy it without knowing what it needed.
As to food, depending on its size, lighting, and placement in the tank, you might not need to feed it anything. However, because you're running PC's, and your ignorance of the animal, I will assume that you don't have adequate lighting, which means that regular supplementation with phytoplankton is your best bet.
Please do not ever buy another animal without checking in on Reef Central first to know what it is you're getting into. Sorry if I'm being harsh, but we've seen this so many times, where people buy animals and kill them through ignorance, that it's what gives our hobby a bad reputation.
Thanks!