Before you begin you will need the following things:
plank of wood
[optional] black vinyl duct tape
[optional] cement & bucket
Note: I live in Australia If you live in an area where it snows you may have to take other things into account for your fish to survive. Koi fish also need specific habitats that I have not addressed in this tutorial.
My total cost for this project was around $100 as I only needed to buy the liner, sand and the pump. The pond liner cost me $40
Step 1: Step 1: Digging the Hole
You want to dig the sides straight down, but be careful that you don’t break off parts of the wall as we want them nice and solid for later. You might want to start a little smaller than your ideal size and make it bigger as you go just incase you do accidentally collapse part of a wall. One point to realise is that once you have put on the rocks at the end it will seem smaller so don’t be afraid if it looks really big right now.
Take off the crumbly top soil to a width of 4-5 inches around the hole if this is an issue for you like it is for me. The top soil for us was only about an inch thick, which gives us a solid foundation for the bricks. Use a straight plank of wood and a spirit level to make sure your sides are reasonably in line across the pond. Use a hand trowel to shave off a little more if some areas are higher than others.
Create a deep part and a shallow part in your pond. The centre of my hole is about 15cm deeper than the small area at the top. This will allow us to put in a range of plants as we desire. Some plants can only be placed in up to 20cm of water, some like it a lot deeper. Think about the fish you are going to get when you are planning your size as well as Koi need a much deeper, larger area than other fish.
Check for rocks and roots that may puncture your liner. After scraping with the shovel and removing most of the rocks I used my hands to feel around all the areas of the pond and dug out any more small rocks with the trowel.
Next, place your underlay in the hole. I used about an inch of sand in the bottom and on the ledge. You can also use damp newspaper, carpet or special underlay that you can buy from garden centres.