New pond drained already - help please!

[Aflynn4]

Hi,
We have just bought a house that had a small garden pond - see photos. It was very green!
I opened the filter up, cleaned the gunk out and took out the sponges and plastic meshy balls at the bottom and cleaned them all. I think reassembled the filter and added Blagdon green away for ponds.
Today, the pond has basically drained away!
I don't know what's happened.. from googling I wonder if it's an air lock somehow as I just opened the lid of the filter.
Please can I have some help and advice. Have attached photos of pond and filter.
Thank you!

 

[j.w]

and welcome @Aflynn4
Not familiar w/that filter so I just don't know.

 

[Aflynn4]

I think it's possibly a hozelock one ?

 

[mrsclem]

Is the area around the filter wet? The lids on those filters have a gasket and have to be locked down or they leak. This is about 3rd time I have heard of this problem.

 

[addy1]

Welcome to the forum.

I always coat the gasket with silicone grease before closing it up again.

 

[Lisak1]

The water had to go somewhere - figuring out where would be a good first clue!