On 6/4/2010 12:58 PM, Chip wrote:
On 6/4/2010 5:04 AM, wrote:
if you got
rocks or gravel down there get them out and throw them out.
I know this group and virtually every serious koi ponder says-NO rocks
in pond. For cleaning this is great, but there is a substantial faction
that says rocks and gravel are good and house good bacteria to help
clean up the bad stuff. Almost all in-house aquaria have lots of gravel.
What's the real skinny?
Chip
Chips right. This has been a long running debate. In fact, I've saved a
version of this debate from the old rec.ponds group before the trolls
took over. Read over and form your own conclusion.
The bottom may be lighter in color, but often times this light rock gets
covered with dark green algae, which defeats the intention. The gravel can
get covered with mulm, the dark organic material that is a byproduct of the
natural biological functions of a pond. The mulm can totally or partially
obscure the bottom. Hence, it is an open question how long the bottom will
stay pristine.
As for the aesthetics of the gravel. There is not discussion on taste so
this becomes no real argument for or against this question.
The third point is then the most critical and most contentious. With a gravel
bottom the mulm, fish waste and decaying plant matter from the pond does
not flow
quickly to the drain or sump, where it can be removed from the pond. The
gunk gets
trapped in the spaces between the stones and there it sits.
In a properly designed pond the solids produced in it are carried by the
flow of the water down to where the pump can suck the material out and send
it to the filter system where it belongs. (Please note that I do not imply
that a pond with gravel is by definition poorly designed, for there are many
smooth bottom ponds whose specifications do not add to its efficiency.
However, I do say that no matter what the design, gravel degrades the
efficiency of a pond).
What then, is the detrimental effect of having gravel. The first thing to
remember is that a pond is not an aquarium outside. Gravel, used in an
aquarium has a purpose, it acts as part of the filter system. Water is
drawn through the gravel, mechanically removing debris and providing a
surface for aerobic bacteria which neutralize ammonia and other byproducts
of the aquarium system. The water is then pumped back into the tank.
In a pond there is not under-gravel filter. Water is not drawn through the
stones, it passes over the top and the mulm that accumulates under and
between the pebbles builds up in an oxygen deficient environment. As a
rule, aerobic bacteria are beneficial and anaerobic bacteria are not.
Anaerobic bacteria survive without oxygen and their byproducts are often
harmful, such as sulfur dioxide, the chemical that give a rotten egg smell.
In addition to these bacteria, other harmful organisms fester in the goo at
the bottom of gravel ponds.
To counter the foulness of the gravel bottom, practitioners say that
chemicals can be used to reduce the mulm to an inert material. There are
other products, such as PondZime which reduces the mulm with enzymes. The
efficiency of these remedies is questionable, not to mention that even if
the crud is neutralized it still continues to accumulate. Hence, more
chemicals must be used to deal with the problem. It seems that a much
better, less costly, and far preferable solution is to have the pump remove
the gunk.
Here, a counter argument says that the mulm is only deposited in the filter
and so it doesn't matter where it sits, in the filter or on the bottom, it
is still in the pond system. This argument fails when the mechanisms of
filtration are known. For in a filter system, water is passed though the
filter, supporting aerobic bacteria just as it is in the under-gravel filter
in an aquarium.
So the issue comes full circle just as water is pumped from a pond, just to
be filtered and returned. The idea of having gravel comes from aquariums,
but as ponds are different than aquariums the function of the gravel is
shifted to the filter system in ponds. Ironically and in opposition to the
logic of some ponders, the gravel becomes detrimental to the pond.