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Designing the Project

So we have now got our outline plan, and we have raided the Piggy Bank to finance it, so lets get down to the nitty-gritty of how we are going to do it. From here on its mostly 'either' 'or', its just a matter of making your choice and sticking with it.  So lets run down the list

  • Height:               --  Above Ground, Below Ground or Half & Half
  • Barrier:               --  Waterproof Membrane (Liner) or Sealed Concrete
  • Circulation:       --  Bottom Drain/Gravity Feed or Pumped Surface Flow
  • Filter:                  --  Open Chamber or Pressurised.
  • Water Return:   --  Mid-water or Water Feature
  • Top-up:              --  Manual or Automatic
  • Waste:               --  Mains sewage or Manually Controlled Pump
  • Height:  Are we going to dig the pond down so that the finished water level is at ground level?, or are we going to build a retaining wall up about a metre so that we can rest or elbows on the top and view the fish at chest height?  The third option is to dig down about a metre, and then build a metre high wall around the hole. That way we can have a 2 metre deep pond without the having to go down to far.

    Barrier:  This is of course what keeps the water in.  We can either use a high quality plastic liner, or we can pour a concrete base and build block walls which are then sealed to make them watertight.  Many purists regard the plastic liner as the armatures or 'Poor Man's' option and dismiss it out-of-hand. However many of  today's liners are state-of-the-art and offer excellent quality and a 25 Year Guarantee.  Block on the other hand is heavy and difficult to work,  it is also very expensive to build and seal. It can be sealed by painting with various polyurethane sealants, but for a real lifetime guarantee Fibreglass is the premier option. It is also the most expensive by a long, long way.

    Circulation:  Our next decision is how are we going to circulate the water from the pond. Bottom Drains are fitted to the floor of the pond and piped underground to the filter system. From there the water is pumped back to the pond. As the water is pumped out of the filter system the level falls and is replenished by water flowing under gravity through the bottom drains.

    The alternative is to pump water from the pond to the filter system and allow it to return back to the pond by gravity.  Both systems are equally effective provided safeguards are installed to deal with blockages.

    Filter:  The are numerous designs of filter system but the all fall into two categories, Open Chamber or Pressurised.  The most common, open chamber, passes the water through a series of chambers filled with a variety of media. The first chambers are usually designed to trap solid waste while later chambers provide biological filtration.  This type of filter needs to be quite big to function efficiently, but is simple to construct and cheap to operate and maintain.

    Pressurised filters can be very efficient for their size.  They operate by forcing water under pressure through a relatively dense filter medium which is more effective in removing particles from the water. They are often sealed during manufacture with no user serviceable parts inside and incorporate a back flush system for cleaning.   The drawback with this system is not only the higher equipment costs but also the running costs involved with high pressure pumps.

    Water Return:  Again this is down to personal choice. Many Koi keepers believe that drawing water out through bottom drains and returning at, or below mid water level helps to maintain stratification during the colder winter periods.  Others prefer to make a splash with a waterfall or other feature

    Top-up and Waste are worth considering at this early stage as it is very difficult to make changes later in the construction phase.  Top-up is fairly straightforward with a ball valve being fitted at finished water level. If water is drained from the pond the ball valve falls and  allows fresh water from the household mains to refill the pond.   How we drain water from the pond is our next consideration.  We could bale it out with buckets but I am sure that there are few pond keepers up for that idea.  We could of course pump it out into a drain but this needs the expense of an electric pump.  By far the best option is to plumb the waste into the mains sewage system.  Opening a valve is all that is required to dispose of the accumulated waste from the filter system, its quick, clean and efficient. 

    Some may consider this last section to be somewhat frivolous and an expensive luxury. But stop and think for a moment.  I did say at the start that in many ways ponds are just like aquariums, and need the same maintenance schedule.  Well any 'Good Fish keeper's Guide' will recommend small frequent water changes to help maintain good water quality, typically between 5% and 15% per week.   That's easy for a 3 foot fish tank, a couple of 2 gallon buckets is all that's required.  However it's a totally different proposition for the pond owner with thousands of gallons to contend with.  My advice is get it right now or the pond will become neglected because of the constant chore of maintaining it.

    Koi and Goldfish in a Garden Pond