Actually, having to target feed clams under 2" is much more myth than fact. First of all, a 2" gigas is in a very different stage of life than a 2" crocea. Second, you should never target feed any clam. It's just not healthy for them.
On the other hand, I agree that you don't have to feed the tank phytoplankton in order to keep a clam healthy. 99% of the tanks out there have plenty of food in the water column for the clam. Like Jin said, let the water clear before you add any more phytoplankton, and then if you decide you want to continue adding phyoplankton (I'm a fan of feeding my tank phyto, personally), once the water clears, try again with half your normal feeding.