Just to give an update - the experiment failed...
After a while the bottom leaf fell off./ I must have been due to rot, as it was still healthy and green when it just dropped off.
I took it out of the fish tank, and repotted it in clay pellets. I let it dry out and watered sparingly. I stuck it up on the top shelf, where I rarely look and had actually given it up for dead, cos it only had 2 leaves left and zero roots.
So I was pleasantly surprised last week, when I saw a new leaf growing. It's getting bigger everyday.
Orchids sure are tough little things
