Thanks for that.
Do I need to break the concrete at the bottom to allow for drainage? I'm planning on paving that area off and maybe putting a garden swing there so maybe hardcore is a good option?
Recently bought a house with a fairly large pond in the garden. The previous owners have removed the fish and emptied out the water, and now all that is left is a roughly 10-15cm thick layer of green slimy junk at the bottom of the pond.
My aim is to pave over it. Not interested in turning it...