I have it up as high as possible and he is planted pretty good. So I'm afraid it might fall.Keep it in good lighting and don't try to pry him off a rock if his foot is planted
I like ESV Dried Phytoplankton there is a powder one and a small bit one I like the powder better.
Good thing is you got a clam that is the right size really, above 3 inches you have a much better chance of survival. I have two clams one is 9 years old and one is 8 or maybe it is 8 and 7....I don't remember...in any case starting size is important. Maximas do better attaching to rockwork if you can place something flat under or they sell little man made holders that they can latch onto they have better chance of survival. The thought is the opening they have for the foot can let in parasites or other baddies if not attached.