Left: Loose rock on the bottom of a pond, covered with opportunistic
algae and choked with organic waste and debris
Note the unhealthy
condition of the lilys. They are being strangled by the algae.
The "loose rock" style of ornamental
fish pond construction has become very common in the United States. This method
of construction dictates: (1) "loose rock" lining the
entire bottom and sides of the pond, (2) lack of bottom drain,
and (3) the dependence on pump suction to remove waste and unfiltered
water through a surface skimmer. (4) The folds in the pond liner
are left as they are created when the liner is placed in the
excavation site. (5) The "loose rock" is continued
up into the waterfall and expanding black foam is injected into
the areas under and around the waterfall spill rock to prevent
water from running under the rocks rather than the preferred
path over the rock. Most of the waterfall rocks are left loose.
It is claimed
that the "loose rock" environment creates a large surface
area on which beneficial bacterial growth occurs. This - in the
short term - is correct. Unlike water in a natural stream bed,
which has contact with the earth and a myriad of bacterial processes,
the water in a lined pond is confined from this biological activity
by the liner. Over a relatively short time, organic waste (mulm)
from the restricted bacterial activity in and around the rock
surfaces builds up and has no place to go. Non beneficial, opportunistic
algae use this nutrient (mulm) and compete with other pond inhabitants
(fish) for the available oxygen. In this scenario, algae always
wins (eutrophication)*. Fish can begin to show signs of stress and eventually koi
fish behavior can be altered.
* Eutrophication: The increase in nutrients results in a massive increase of phytoplankton growth, termed a plankton bloom. This bloom decreases water transparency, leading to the loss of submerged plants. The resultant reduction in habitat structure has negative impacts on the species that utilize it for spawning, maturation and general survival (Koi). Additionally, the large number of short-lived phytoplankton result in a massive amount of dead biomass settling into the sediment. Bacteria need large amounts of oxygen to decompose this material, reducing the oxygen concentration of the water.
It is common
to hear that this style of pond "looks more natural".
However, once the rocks become covered with opportunistic algae
and choked with mulm, the visual effect becomes one of increasing
organic waste and loses the colors and attractiveness of natural
a huge number of calls every year requesting assistance in managing
these problems. These callers complain that: (1) their ponds
are full of algae, (2) their fish are not thriving, (3) they
are having to put many more hours of maintenance into their project
than expected, and (4) feel their time and money have been wasted.
the visual definition of any rock placed below water surface
is, for the most part, lost to algae and debris after the first
six months of operation, our preferred method includes: (1) no
rocks below water surface of the pond, (2) mortaring in all rockwork
in the waterfall and border edge and (3) taping flat the folds
of the liner.
A pond created
without rock below the water surface dramatically reduces maintenance
levels. The pond is free of the huge bed of waste-collecting
"loose rock". The unobstructed liner surface is clear
and free of collecting waste and the free flowing current over
the smooth liner surface towards the bottom drain allows for
simple and efficient removal of waste. For additional information
on drains and other minimum maintenance construction components,
please also read "The
Art of Planning".
rock" ponds typically use skimmers for unfiltered water
intake. Surface skimmers only address the surface waste and do
nothing to collect the heavy solids that sink to the bottom.
Ponds with complete emphasis on surface skimming all water essentially
act as large settling ponds, further compounding unremovable
waste from the floor.
described process degrades the general water quality and increases
the maintenance levels for the pond keeper. Minimum maintenance
can be achieved with some modifications to the existing installation.
The need for a bottom drain or initial water intake system at
the deepest area of the pond becomes paramount. Since complete
rebuilding of the pond is often not an option, retro fitting
can prevent spending additional thousands of dollars and countless
hours of upheaval to the landscape.