Angling the base
Once you’ve completed your walls, it is time to considered angling the base of the pond.
The main reason for this is so that any waste from the fish, debris and such will be move towards the bottom drains, and then removed by the vortex chamber. In this manner it would not accumulate at the bottom of the pond or any of the covers
Again, use a concrete mix of 3 parts chippings, 2 parts sand, and 1 part cement.
Make sure that you leave the bottom drain raised high enough as the base will also be rendered in the same way as the walls.
Make sure that the concrete is reasonably dry when you shape it
Even if you have deep water returns, you should still have an angled base, because unless your returns are efficient, you will end up with lots of debris lying at the bottom of the pond. This will be a hassle to clear for maintenance.
Rounding the corners
Rounding the corners of your pond will help you ensure that debris won’t accumulate at the corners.
It would also encourage a good flow of water in the pond and prevent fish from swimming into the corners.
A 18″ x 9″ x 4″ block can be used to build up the corner. Fill in the space behind the blocks and sides with cement mix.
For smaller ponds, use a standard size brick instead of a concrete block.