Well supposedly smaller clams don't contain enough zooxanthellae to sustain themselves so they need to be feed with phyto. That's what I've heard but someone can correct me if I'm wrong.
They are much harder to keep but still possible. Local friends have never had luck with the very small ones. I have seen countless amounts die overnight in optimal conditions. I would shoot for atleast a 2.5-3" if I was you. It's still small and will have a much better chance. Much to popular belief clams are not easy to keep.
I got mine at around 1.5" and its still healthy and kicking nearly a year later. It's around 2.5" now and doing well. I feed the tank phyto and coral foods every 2 days with some powerful lights.
A clam in a 3 gallon tank will have to be monitored very closely for changes In parameters. May be difficult but possible. What type of lighting you will have on that nano
Thanks for all the tips n for believing lol. I got a beamswork led and two minor led clip ons. Light is strong n got two hang ons one pretty big with a built in skimmer. Called azoo mignon skim. Also a 75gph pump inside. Seems like maxima s r hard to find these days