Why are all of my clams dying???

[Delphinus]

Unfortunately ... this is hugely common. One of the worst things for a clam is to be in the same tank as another dead clam. If one goes on you, you have to get it out right away otherwise it kicks off a chain reaction. Basically you have to cull them before they're actually dead if you think they're past the point of no return. It sucks. I've lost 5 or 6 in the last 3 months myself and they were all >5 years in my care so I've been seriously hit hard by the losses myself ... I know your frustration.