Whats wrong with my Clams?

[MarkoD]

Suggestions would be welcome if someone knew what the issue was.
I was expecting someone to know why they're closed and then offer a solution.

Not offer 5 different solutions to be done at once.

So I'm going to do them one at a time and first I'm going to try and rule out a fish picking at it.

I just find it hard to believe that these clams are fine for 6+ months and then one day they just decide its no longer good enough at the same time. While nothing else in the tank is effected

[MarkoD]

The reason I chose a large tank with a large water volume is to eliminate drastic swings and water changes. Water conditions don't change at the snap of a finger. If the water conditions were deteriorating, it would be a gradual process and I would have noticed it.

[Proteus]

Originally Posted by MarkoD

I just find it hard to believe that these clams are fine for 6+ months and then one day they just decide its no longer good enough at the same time. While nothing else in the tank is effected

Clams are not coral or fish