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Page 5 of Build a Fish Pond Continued...

Component 8 - The UV

The purpose of the ultraviolet water clarifier is to sterilize free-floating algae so that the water does not turn green. The bead filter will take out the dirt and make the water healthy but the water will not be clear without a properly sized and installed UV unit.

UV’s are sized by wattage and wattage is determined by amount of water and a few other factors such as amount of fertilizer (fish waste) in the water and sun. For example: a pond less than 300 gallons would use a 9-watt UV. A 9-watt unit for 400 gallons in the shade might work but if the pond is in direct sun all day a 9-watt UV will not keep it clear. We do not suggest you rely on the manufacturer’s suggestions. They tend to exaggerate effectiveness and usually the size determination is based if all factors are optimum. Do not make an expensive mistake by under-sizing the unit.

The UV is a PVC plastic cylinder with two openings so that water can pass from one end to the other. The water passes over a quartz sleeve inside the cylinder where a lamp is encased that emits ultraviolet rays. The lamp is attached to the electrical transformer and the end screwed hand-tight.

You would not believe the number of folks who ask - so here is the answer: No, the UV does not go under water - not unless you want to fry your fish or yourself. Okay, there is one exception but it is not the type we are profiling in The Doc’s Dream System.

The UV is most effectively installed after the bead filter. In many cases it cannot be installed directly into the main return line because the water will flow too quickly through the unit to make it effective. A bypass must be constructed so only a portion of the water passes through the UV. This is most effectively done with PVC.

build a fish pond A tee is placed in the PVC line and a short piece of PVC is run to one opening of the UV cylinder. It does notThe quartz sleeve and lamp of the UV are both very delicate. Whenever handling and while installing the unit be very careful not to break them. The slightest crack in the quartz sleeve can allow water to seep onto the lamp and short out the system. This also can void the warranty. matter which. The other opening runs back to another tee that is installed in the PVC main return line. The two tees are separated by a gate valve (Component 8a) so that the amount of water that flows through the bypass can be controlled.

The quartz sleeve and lamp of the UV are both very delicate. Whenever handling and while installing the unit be very careful not to break them. The slightest crack in the quartz sleeve can allow water to seep onto the lamp and short out the system. This also can void the warranty.

Design Tip Quick Disconnects installed into the UV bypass will make it easy to remove the unit so that you can store it inside during the winter to protect its delicate glass parts. It is also a good idea to install quick disconnects in the plumbing at the intake and discharge (pressure side) of the pump.

Koi Pond Picture

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Component 9 - The Water Return

Once the UV is in place it is time to return the water to the pond. The return line must connect with the line already run to the induction jets installed in the liner wall of the bottom, main part of the pond. Only a portion of the water will go to the induction jets so either a tee or a Y should be installed in the return line and gate valves installed to control the amount of water. In our diagram we chose to place the gate valve on the line going to the induction jets after the tee. (Component 3a)

There are several different ways the water can return to the pond with dramatic effects. The imagination is the only limitation with how it will look. Here are a few ideas to help spur the imagination:

  • All of these are constructed higher than water level so it may be necessary to create a hill by importing soil. Do not forget to tamper the loose soil down before sculpting out the streambed or bog pond.
  • Wherever there is water there must be liner underneath or the pond will leak! Do not trust concrete. It leaks.
  • Use 1 continuous piece of liner if possible. Piecing liner creates chances for leaks.
  • The liner of the waterfall, stream, etc. must overlap the liner of the main bottom pond.


The hose or pipe drops the pond water into a shallow streambed that is lined with rocks and plants.

  • Do not use sand. It creates a cleaning nightmare. Use rounded pebbles or a liner disguise such as “rock on a roll”.
  • Place a jutting rock or two in the middle of the stream to interrupt the water flow and create rapids.
  • It is okay to pull the plants out of their pots and plant directly into the rocks. They will grow well from nutrients in the water.
  • If placing large boulders on the “banks” of the stream be careful that the weight of the boulder does not push the edge of the liner down lower than water level. It can drain your pond in minutes.
  • Cement rocks together to force the water over the rocks instead of below them.

A Bog Pond

Whether the bog pond is connected to the main pond below by a waterfall or streambed a bog pond provides an attractive planting area that rowdy fish cannot destroy.

  • Plant without soil. We suggest planting in bags of well-rinsed lava rock. Lift the bags (and the plants) out for easy cleaning.
  • Perfect setting for a vegetable filter. One can never have too many methods of filtration.

A Waterfall

Waterfall Picture

Nothing compares to the music of a waterfall. Make it dramatic!

  • Keep the water on top of the rock by cementing the crevices. For example: The water will fill up a bog pond then overflow into the falls by spilling over a large flat rock. Do not allow the water to flow under the rock by cementing the crevices.
  • Create a cave behind the falls to echo the sound of the splash.
  • Line the walls of the cave with rock. Stack rock behind the falls to hide the liner and create a natural appearance.
  • Watch the splash. Water escapes the pond via splashing quite easily. Simply moving a rock can often correct the splashing.

Formal Statuary Fountains

Cement or bronze fountains add elegance to a pond as long as it is not overdone. Most statuary fountains are not designed for the amount of water flow coming from this type of system so the main water return must be split and only a portion of the water sent to the fountain via a reduced water line.

Aerating Fountains

A fleur-de-lis, bell or bubbler in the middle of the main pond can add aeration and a touch of formality. Since the plumbing on this system has been run outside the pond for filtration reasons it makes it more difficult to install one of these types of fountains. It can be done with a little planning by running the return line back to the pond and creating a manifold for the fountain.

Resources: This article is from the Pond Doc's Website.

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