Converting a pool to a pond

Mark Ludwig mpludwig at students.wisc.edu
Mon Mar 3 13:50:54 EST 1997


At 12:26 PM 2/28/97 -0500, you wrote:
>I live in Fayetteville, Arkansas and have a gunite inground pool.  Every
>summer I cringe at the amount of chemicals I have to put into the pool (and
>back flush into my yard!).  I'd rather use it for rainwater harvesting and
>fish production if there was some way to keep it clean enough to still swim
>in.  Have anyone tried such a conversion or have any ideas about how to do
>it?  Thanks, Rebecca Bryant
>
Hi Rebecca, a fine goal, and a few thoughts,
The way ponds stay clean is to convert the excess N and P in solution to
plants.  A "dirty" pond is usually clouded with algae or possibly bacteria
exploding in population due to a algae die off.  Your best bet for a clean
natural pond is to limit the algae growth by growing some type of agressive
vascular plants.  Floating plants are great for this, and water hyacynth is
probably the king here, but its highly invasive in your subtropical setting
and may be illegal to posses in your area.  Many of the other floaters like
the duckweeds (lemna sp.)  will be unpopular with swimmers as they will coat
you with tiny little leaves as you emerge from your dip.  If you are willing
to add a layer of washed sand to the bottom of the pool you could add rooted
plants to the mix.  I would not add pond mucks or fine soils as they will
almost certianly lead to turbid water and increase the fertility level of
the water.
Another approach could be the construction of a "living Machine" where your
exising pool filter pump gets diverted through a series of artificial
wetlands, allowing the plants and filter feeding animals therein to do the
scrubbbing for you.  This has been proven highly effective by the Earth
Island Institute (in Boston MA I think) in sewage treatment, so your needsa
can almost certianly be met.
The inclusion of filtering animals (clams, daphnia etc) will help reduce
cloudy waters greatly.  In the Great Lakes, the unfortunate outbreak of
Zebra Mussels has cleared the water in many areas to near pre europeon
settlement levels ( but don't put those in your pond OK?).  I would also
include some kind of agressive surface feeding fish to control mosquitos
(like the misquito fish - Gambusia Sp).  
Remenber to consider that each bit of food you add will increase the N load
in the pond and that removal of plants and animals will reduce it.  You may
find that you can harves a lot of biomass from the hyasynth plants for
mulching.   If you have both floating and rooted plants, keep the surface
cleared off somewhat to allow loght penatration.  Keep in mind the need for
Oxygen in the water which disoloves in from the surface, and don't overstock
with fishes.  Warmer water has less ability to absorb oxygen, so plan your
harvest appropriately.  Agitation or areation will help keep O levels up, as
will plants to some extent.
Consider where your selected fish species will feed.  Bottom feeders may
make a horible mess of the water by churning the bottom while top feeders
may eat all the mosquito fishes.  Consider establishing a good base of food
species before adding the fish you plan to eat.
Last but not least, consider much of what I say here suspect and talk to
your local extension and university folks if possibe to confirm my
ramblings.  ;<)
Mark



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