Concrete Pond Construction

Q. I understand using a water meter to measure the total gallonage of the pond and filters but I have no idea how to measure how many gallons per hour will be passing through the system so that I can control it.

A1. The way I did it was to mark a bucket at 2 gallons and use a stop watch then do the calculations on how long it took to fill the bucket with the amount of water in the pond, this will give you some idea of how long it takes to turn over the pond and you can adjust your pump flow as required. Posted 27.11.05 by Susan.

A2. As an alternative to the measuring the time taken to fill a bucket etc. If you have an external pump, connect, with "T" joints etc, two pieces of clear vinyl tube as close to the pump inlet and outlet as is possible. Mount these tubes so that they 'stand' upright and side by side, switch the pump on and measure the difference in height of the water levels in these sight glasses. The difference is the "head" that the pump is having to develop to generate the flow. On the pump's flow chart look up that head up and the corresponding flowrate.

A3. Another but expensive way to measure the flow is to use a flow meter.

Q. My understanding about the various pipes that come into the pond is that they should be cut flush with the fibreglass. Is there any risk of fish trying to swim into those pipes?

A. Any mid-water or deep water returns should be cut flush with the fibreglass so that the fish do not damage themselves against the edge. It is only 1.5 or 2 inch pipe the fish should not swim up the pipe even when the pump is switched off.

Q. Should the overflow pipe also be flush with the wall or can it stick out a bit so that I can fit something on it to prevent fish from swimming out if the water level rises too much?

A. The overflow pipe is normally fitted in the last bay of the filter so there is no risk to the fish.
The overflow pipe should enter the filter some 4 inches below the water level and fitted with loose fitting bends so you can adjust the height of the water before it overflows.
If the design of the filter does not allow this then it can be fitted in the pond and the same applies. In this case you can fit a plastic grid over the pipe to prevent fish swimming into it.

Q. Books and web sites go into detail about filtration,but I have not been able to find out what to do if my pump stops working due to a power failure. Any advice gratefully accepted.

A. If your pump stops for a couple of hours there should not really be a problem.
It is very important to ensure that your pump will be able to prime itself when the electricity returns, and it is worthwhile checking this out before you have a power cut. If you are there when there is a power cut in hot weather then you can use a garden hose with a fine spray to spray water on the surface to add oxygen. If you have air stones in the pond and filter it is a good idea to have the electricity supply coming from a different connection to the pump. Then if the one RCD trips out for any reason when you do have an electricity supply then air will still be supplied to the pond. These things always seem to happen when you are out of the house.

Q. I see that a lot of your members use central heating pumps.What do you feel are the pro's and cons of these circulators?

A. There are many types of good pumps on the market now and really central heating pumps should not be used. They do feature on many ponds on this website, but those pages were made up many years ago and most have now been replaced with different pumps.

Q. Regarding the returns, I've positioned these today as follows. Because the pond is an elongated quadrant I have three (albeit benched slightly) right angled corners. I've positioned a 1.5" tank connector (to penetrate and seal the liner) around 12 inches away from each of these corners. As the connectors can accept a 1.5" pipe inside the pond I was going to fix a 90* bend plus a 6"ish pipe to it and direct it down slightly and into each corner to 'hose' any debris away. I am planning to make all returns point clockwise (as in one of your articles) to produce a circular flow. The 4th return is on the curved (and longest) wall and to this I was going to fit a venturi. The skimmer will be fitted in the opposite straight wall so hopefully the disturbance from the venturi will push floating debris across to the skimmer box (again as per a diagram on your site). The returns will be 20"ish below water level, do you forsee any problems with back pressure to the pumps.

A. I have not quite worked out what an elegated quadrant is. Why are the pipes 20 inches below water level. Nine inches is the norm as the venturi will lose a lot of efficiency if any lower. It is advisable to use 45 degree elbows as they do not restrict the flow as much. I do not see any point in a 90 degree elbow and a six inch pipe downwards as this will greatly restrict the flow. It is better to have the flow as you say clockwise and if the flow is directed slightly downwards then the natural movement of the water will keep debris moving towards the bottom drain, although this is more difficult with a liner due to the creases etc. The venturi adds important air to the pond, but a straight pipe well below the surface does not, unless you have a very powerful pump. I would use a venturi on each outlet. Are you using push-in pipe fittings? If push-in then that is no problem regarding alignment. If using pressure pipe then at least one joint should be threaded so you can move and adjust the pipework holding the venturi. It is necessary to fine tune the direction of the pipework holding the venturi when everything is up and running and can take several days to perfect it.

Q. Which type of pipe should I use as I have been told so many different things . Some have said use ring seals as this will be more flexible if I have any ground movement . Others have said PVC solvent weld will last longer , and others have said use ABS as this is more stable and less likely to crack due to temperature changes . I have ruled out the ideal option of pressure pipe as I have a limited budget.

A. There are many conflicting ideas on what pipework to use.
For the 4 inch pipe (110mm) then most koi-keepers use the orange underground pipe with solvent and as it is surrounded by concrete this is quite satisfactory.
For the pipework for the pumps then I feel it is important to use pressure pipe. However this is expensive and an alternative is ABS pipe which is thick and is used in most swimming pool installations.
You can buy white solvent pipe from Wickes which seems quite good, but we do not know for how many years it will last.
I would not recommend ring seals, but if you do decide to use that then the joints must also be secured by stainless steel self-tapping screws.

Q. I have a site that involves a 10 foot drop from top to bottom of where I'd like the waterfall to begin and where the bio-filters would be located. Can you advise how such a pond should be plumbed? The pond is in the middle of the vertical drop.

A. You have a choice of either pumping into the filter and gravitating back to the pond, or gravity into the filter and pumping to the waterfall. You cannot pump into the filter, and also out of the filter as the second pump will run dry or the filter will overflow.
In the first case (pumping into the filter) then the filter will need to be above the waterfall. The water will then gravitate out of the filter and into the waterfall. You will need to have some additional pipework as you do not wish to run the waterfall in the winter as this will only cool the water.
In the second case (gravity into the filter) the filter will need to be level with the pond. You will need to excavate part of the hill. or build up the lower part. You can then pump from the outlet of the filter up to the waterfall, or back to the pond in the winter. For this you will need a pump such as a swimming pool pump that can pump under pressure and still deliver the quantity of water.