Koi Pond – Building Walls Around the Pond

Building Walls Around the Pond

Once the concrete base is completely dry it is time to start building the walls around the pond.

You have the choice of using concrete blocks that are 18 x 9 x 4 inches in measurement and lay them on their side so that the wall is 9 inch wide. Or you can choose to use hollow concrete blocks to form a very solid wall. However, remember that these 18 x 9 x 9 blocks are very heavy, and difficult to lay. What you should do it to lay these block up first then pour the concrete into the holes, thus cementing the blocks together. If you are using these blocks you can reinforce them with vertical reinforcing bars previously discussed when laying the concrete base for the pond.

Your mortar mix should be 3 parts sand and one part cement. Do not smooth out the wall completely as the roughness will help in the render coat you will apply later.

When going around the corner

When you build an informal pond, you may need to split the blocks and arrange them in a way that they curve around the areas that you want them to. Alternatively you can use the smaller fired bricks to build those corners in between the concrete blocks.

Once you’re done with the walls, you will need to back fill the back of the wall with chippings or stone dust.

What goes on the walls

You will definitely be including some pipings and items into the walls. So this would be the best time to decide what they are and to start installing them in.

  • Power skimmer

The power skimmer works to remove leaves or debris from the water surface of the pond. They do make a difference in terms of the clarity of a pond. You can have the choice of having a skimmer that sits on the wall or one with an extended throat that is situated away from it.

If your pond is level to the ground, dig a shelf for the pond (when you’re digging out your pond) 7 inches below water line and the width of the skimmer filter, compact the earth, then position the skimmer unit on this opening. You will want marked water level to meet the skimmer ¾ inches below the top of the unit. Ensure that the skimmer is level with the pond and tip it a quarter inch towards the pond. Make sure that the skimmer is flush with the coping shelf behind the wall of the pond. Then fill around the unit with moist sand, and hand pack every two or three inches. Do not compact them too hard.

If you are installing a pond that has a ledge higher than the surface of the ground, build your wall and allow a space width of the skimmer to sit snuggly on the ledge. Arrange the skimmer so that the water level in the inlet should be 75% of the total opening. Cement the skimmer into position.

You should add some type of grid over the opening, so as to prevent fish from inadvertedly going into the skimmer. Use non-toxic materials to create vertical bars around the skimmer opening. You will need to drill the skimmer to accept these modifications.

  • Pipework

There are various pipings that you will need to consider installing as the walls are being built.

You will install pipe for the power skimmer, as well as another for the water return from the main pump.

You may also include a deep water return, which must be fitted at an early stage at about three feet below the water surface.

  • Waterfall

The sound of running water can have a very calming effect, and some koi owners might like to have this feature in their pond. If that is so, then you will have to start constructing the feature while the walls are being built before the final rendering is done. You need a flow of water that is at least 1,000 gallons per hour to have a successful flow rate. If you go for a wider waterfall, you will need more. Take into consideration also the height of your water falls as they can be very noisy.

If you leave in an area that has seasonal weather, you should shut off the waterfall over winter as it will lower the temperature in the water if left running. Use fiberglass to coat the waterfall if you have used cement to seal in the lime.

  • Deep water returns

Water returns that were incorporated into the pond in the 80s sat about three feet below the water surface, and were designed to cause perpetual movement to the water. This in turn ‘forces’ the fish to swim against the current as they would naturally in their environment. This system though, requires a pump, and the rate of success was fairly low.

In new and current ponds you will find this feature, but it is now fitted low in the wall of the pond at a 45 degree angle downward and at a diagonal cut. This is so that it would create a whirlpool at the bottom of the pond, moving debris towards the bottom drain which is then removed.


Deepwater returns are placed to ensure there are no dead spots in the pond, which is important especially in hugs ponds and when you are treating the pond – it makes sure that there is effective mixing of the treatments that you use.

Providing the fish with a current to swim against is also good for them. The deepwater returns also provide additional aeration and gas exchange as well as the above, keep debris moving to the drains for removal by the vortex chamber

The bigger your pond the more deepwater returns will be required.