air is a problem for this kind of clam? I thought that was for the giant sea clams like maxima and crocea. These little bivalves don't have a shape that really lends to trapped air. They can 'burp' themselves when they're healthy enough to move around.

The electric clams are hit and miss... they don't have a long life span compared to other critters we keep in our tank, and there's no telling how old they are when you buy them. They are delicate, sensitive to fluctuations that happen in newer tanks, and difficult to feed even in established tanks.

I've had 4, one lived over a year, the rest a few months or less. Do some research about their diet, the way they attach, life span and growth, and you may still find that you didn't do anything wrong.

If the shell is loose, it's not a good sign, sorry - that muscle needs to be strong for it to survive. They're active at night though, so if you want to be sure watch to see if it opens up a little in the evening. Don't wait too long to remove it though - dead clam is rank and terrible for water quality.