Clams and water flow

Do clams require any specific amount of water flow? I guess I have never thought about it much since they have been in the 265 with pretty high flow, but since I'm doing a clam only tank now I'm wondering. It will be fed off the 265, but wasn't really planning on having any powerheads or anything in the tank.

So my question is...as long as they are getting some water flow for 02 and for plankton to feed on does it really matter?
 
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