I am re-housing my koi in a deeper purpose built pond with bottom drain - I will keep you informed how it is going as soon as I get the web up to date.

The two photos Opposite show the bottom drain trenches dug out ready for the bottom drain to be concreted in and the floors ready to be concreted/sanded to give a smooth surface for the box welded liner to lay on. So guess what I will be doing for the next few weeks.

You may wonder about the walls - I intend to line these with polystyrene blocks both to smooth out the surface irregularities and act as insulation.