I'm an Idiot

[tang daddy]

Originally Posted by sully08

I thought ich can only be spread through fish, not transfered any other way,

The life cycle of ich is they feed on the fish then detach and lay offspring in the sand, then swim in the water column and reattach to other fish. It is very possible that they don't only remain in sand, sometimes also on coral rubble.

In Maries case, that is exactly what happened!