I now have a lid switch fitted to the aquarium (a waterproofed reedswitch triggered by a magnet in the lid flap)

And I have done a load of work using the time loops I implemented in v2.0 to add reminders for Feeding, simple beeps and a message after 24 hrs, more aggressive beeps and message after 48 hrs. Opening the lid clears the message.

The lid plays a tune when opened and beeps periodically as a reminder until closed.

When the lid is open pressing the button triggers a maintenance mode which fades the light rapidly off and disables the fan until the lid is closed, 

Finally; long pressing and holding the button when the lights are On rapidly decreases the on timer to allow a shorter off period to be set if power was turned off during maintenance.

I'll test this on my proto-board and then on the actual tank. If all is good I'll release v2.1 and mark this complete for now.