New to this forum but would welcome some advice.

I have a freestanding Blagdon infinity pond with a small number of goldfish in it, have run it for five years without any issues.

This morning I discovered a pool of water on the outside of the pond and the fish were swimming in no more than 2 inches of water. It appeared something changed within the pond in the middle of the night, and the pump had started pumping water out of the pond instead of back into it. I can't explain or understand how this happened, pond is in a rear garden which remained locked throughout, mesh protection wasn't moved and there's no sign of outside human or animal interference. Also, wasn't windy at all.

Only explanation I can come up with is that maybe a fish swam into the pump tube and knocked it into a different position so that the water pipe was angled differently. But not even sure if a fish would be strong enough to do this? And if so, what can I do to stop it happening again?

Pond is now refilled and is not losing water, so no sign of any leak. Fortunately fish seem happy and no ill effects from the ordeal.

Need more information please.
Where was the pump return pipe, and where is the pump return pipe now?
Have you got visitors staying at the moment?
Was anyone up before you?
Since you refilled and posted on the forum, is the pond still as full as it was?
Pictures always help.