A Small Pond

We had a strip of gravel covered ground that has two tree stumps in it and was pretty much root-bound. Our plants were all in pots and this seemed a good place to put a small fishpond in. Due to the poor soil condition, an above-ground build looked easier and would match our large wooden planter build.

I decided to build a frame using 75mm x 75mm treated fence posts, resting on top of the small retaining wall. There is a serious slope there of around 90mm over the desires 2400mm length. The original idea was to build completely on top of the weed control mat under the gravel.

After some thought, being all above ground would make the height far too tall to get the desired minimum depth of water of 650mm, the top of the pond wall would be up around waist height.

I then decided to dig down about 200mm to gain depth and lower the top edge, but that tree stump was in the way. Having it ground out would be too expensive so I hacked at it with a wood chisel, hammer and small reciprocating electric saw. In the end I managed to get it down to the level where very large roots were branching off so called it a day.

The floor of the pond would be in two levels, half at my desired depth and half at around 400mm – we could use the shallower end for planting etc. The surface of the soil was levelled off by replacing topsoil and compacting it into a two-level floor with a slope midway.

The frame was easy to build and done in the same way as my planter. The posts are screwed together at 250mm intervals with 6mm x 120mm screws, holes were drilled in the post being fixed to allow the screws through. The internal corners of the lower layers were reinforced with steel angle brackets. Some rough calculations showed the force on the length of the lower posts to be around 270kg so not too high I think and it reduces rapidly as the height progresses to near zero at the top layer.

To cater for the slope on the brick wall, the large gaps were filled with offcuts, screwed to the layer above and the remaining smaller gaps were covered by running a length of decking board around the inside.

The top and lower outside gaps were also finished with treated decking. The inside was then lined with some foil-coated insulation sheet that I had left over from the games-room build, this stuff is 5mm thick and extremely tough so should be good to protect from any odd stones etc, it will also help insulate the water from frost etc.

The liner chosen was 0.5mm PVC as pure rubber was too expensive and we have had good luck with PVC in our previous garden. Fitting the liner is a tough job, having a two-level pond floor makes it harder too. Once the liner is roughly in position, water is added to help press it into shape. As the pond fills you need to massage the liner into the smoothest fit you can find, using the weight of the water to help.

Once filled and the liner smoothed out, the top capping planks were fitted and off to the garden centre for some plants, to start with we added an Iris and a pink Lilly. The pump chosen was an “Oase Filtral 3000” which is an all-in-one pump, filter and UV steriliser, it has just enough output to run a fountain or a water-bell feature, we were not thinking of having a waterfall.

5 to 6 goldfish will be added when the water stabilises, the volume of water is around 1300 ltrs and 5 to 6 fish is about the limit for that volume, we could add more but it is doubtful the small filter could handle it which would mean a bigger, external filter, larger pump and so on. At 36W the running costs should not be too bad, far less than the large pond we had at our previous house 🙂