More Than Just a Pond

What makes a koi pond a koi pond?

kent_koi_1According to anyone who has a fish pond
— or calls me to come over and assess his
pond and its issues — all ponds with fish
are “koi ponds.” If you could ask a koi, however,
it would disagree! A koi pond is one that properly
addresses the needs of the koi, no matter what
construction or filtration style the owner desires.
A koi pond is first about the needs of the fish and
second about the aesthetic desires of the owner.

The needs of koi must also be addressed within
the boundaries of the customer’s budget and the profit margin of the professional pond
builder. To address these needs, one must
have a good working knowledge of both. I
believe lack of knowledge, coupled with the
customer’s budget and the profit motives
of the pond builder, are the main reasons
our industry has such a bad reputation. As
I’ve stated in a previous article: with no
codes, specs or rules, 80 percent of ponds
fail within the first year of construction,
and 80 percent of those fail within the first
six months. Our industry needs to clean up
its act, and that starts with knowledge and
ends with integrity.

Basic Requirements

I don’t profess to understand all the
needs of koi, but I think I know enough to
build them a
good habitat.
On a basic
level, koi need
a few things
that promote
a healthy
aquatic environment.
This environment consists of a
minimum volume of water per adult fish,
good water quality, a high dissolved oxygen
content, good circulation and a healthy
diet. It’s also important to keep dangerous
obstructions like sharp rock stands and
large, freestanding lights out of the pond so
the fish don’t damage themselves.

These parameters are arguable and variable
depending on geography, temperature
and overall water quality. But in general,
we can agree on some basic numbers.
Minimum water volume per adult koi, for
instance, can vary, with 1,000 to 2,000
gallons on the high end for those who
intend to raise show quality fish, to as low
as 250 to 500 gallons for those with backyard
ponds. The water volume per koi also
depends on the circulation, biofiltration,
depth, dissolved oxygen content, quality of
food, et cetera. Permanent overcrowding
lowers water quality and requires a tremendous
increase in biofiltration and dissolved
oxygen. Mother Nature will create a fish
health issue in overcrowded ponds, and she
can be very creative as to how she implements
the die-off when you break her rules.

Most under-gravel ponds accumulate sludge that is time-consuming to remove.
Most under-gravel ponds accumulate sludge that is time-consuming to remove.

Depth and Volume

The smaller in volume or shallower
a pond is, the more circulation, filtration
and oxygen per gallon that will be
required for the pond to function well.
Volume and depth are your friend. Smaller
ponds tend to be overstocked and shallow
ponds are dangerous for the fish in terms
of safety from predators and temperature
control.

Our industry suffers heavily from what I
call “shallow pond syndrome.” The 18-inch
to 24-inch depth that some call “standard”
was created by some manufacturers
early on to avoid safety codes created for
the pool industry. This allowed anyone to
become a pond builder, which helped with
sales … but it was not what the fish needed.
Deep water keeps fish safer from predators,
and fish like deeper water where they can
exercise and use their swim bladder more
effectively. Even goldfish like deep water.
Koi like to feed from the surface by going
vertical, so a koi over 18 inches can’t feed
naturally in a shallow pond.

Furthermore, the sunlight affects 100
percent of the water in a pond to a depth
of 18 to 24 inches. Deeper water gives the
system a cushion of water volume relatively
unaffected by sunlight without increasing
the footprint of the pond. Deep ponds
have a more stable temperature and don’t
fluctuate as much between night and day or
when the air temperatures change suddenly
with changes in weather.

Three feet seems to be an industry agreed
minimum in the koi world, and
I regularly build ponds that are five to
six feet deep. Ponds over 18 to 24 inches
require a pool-coded gate and fence, lighting
and egress in the form of steps to climb
out. These are all safety issues and are easy
to design and build into the project.

Quality and Clarity

Water quality and water clarity are two
different things. Water quality is what you
do for your fish and water clarity is what
you do for you. Just because the water is
murky doesn’t mean it’s unhealthy for
your fish … but why spend all the time
and money on a koi pond and not be able
to see and enjoy what you’ve created? A
clear pond can also be unhealthy, so don’t
confuse clarity for good water quality. Fish
eat, excrete and consume oxygen. I consider
myself a “fish poop management specialist”
and design pond systems from this perspective.
When fish eat, they produce ammonia
and solid waste. A koi pond is a decorative
wastewater treatment plant, and your job is
to design a system to act as such.

Two basic types of bacteria (nitrosomonas
and nitrobacter) colonize koi ponds,
establishing the nitrogen cycle which
converts the ammonia into nitrites and
then into nitrates. A mature pond system
should test zero ammonia, zero nitrites and,
in some cases, zero nitrates. Nitrates are
usually removed with water changes. Plants
consume nitrates and in a very mature,
highly oxygenated system, biofilters can house a less-understood family of bacteria
that also consume nitrates. Be cautious
with a too-heavily planted pond for a given
water volume because plants produce
oxygen during the day and consume
oxygen at night, causing stress to the koi.
My pond is 12 years old, has 7,400 gallons
and houses 25 large adult koi, with no
plants and zero nitrates. I’ve built several
ponds that fall into this category. I think I
know why they don’t produce nitrates, but
not in any way I could prove or describe.

Solids must be removed from the system
in real time to prevent anaerobic decomposition
in the pond. Decomposition produces
acids and toxins that are unhealthy for fish.
The filtration system should consist of two
phases: pre-filtration (the removal of heavy
solids from the water column) and biofiltration
(the nitrogen cycle). Each of these can
be accomplished in over half a dozen ways
that all work well. They don’t work well in
every combination, however, so choosing a
pre-filtration method that couples well with
a particular biofiltration type in a specific
style of pond is the challenge.

The Bottom Matters

Most of the dedicated koi pond owners
and builders, including myself, have been
opposed to rock- and gravel-bottom ponds
and tend to build instead with full-flow
bottom drains, mid-water drains and
skimmers on a clean, unobstructed pond
surface. This type of construction requires
out-of-pond pre-filtration that is easier to
clean and maintain. Traditional rock and
gravel ponds, where the water is pulled
from the bottom of the rock layer through
slotted piping and sent to the biofilter, work
well for a short time before they become
overwhelmed. The rock layer and slotted
pipe become restricted and serve as a place
for solids to become trapped. Without good
circulation the system goes anaerobic.

The biggest problem is cleaning them.
The pond has to be completely drained
and the sludge-filled gravel cleaned and put
back in place with all the fish removed to
quarantine during the process. The “once a
year cleaning” is expensive — and it’s never
really enough. Coupled with the movement
of the fish, which is always hazardous
and stressful for them, this becomes a lessthan-
desirable approach to pond design,
construction and maintenance. It’s often
one type of failure in the long list of why
ponds fail. If you are building a pond that
produces anaerobic sludge that must be
removed in this way, you are part of the
problem.

Recently a new type of “under-gravel”
rock bottom pond the industry is calling
the “ecosystem pond” has been promoted
that uses a much more extensive “aerated”
suction grid system with back-flush capabilities.
This method is much more complicated
to construct but doesn’t lead to the
type of anaerobic sludge buildup we’ve seen
with the original systems.

Biofiltration

Biofiltration consists of two basic
categories: non-aerated trapping filters and
aerated bio-reactors. Non-aerated biofilters
are the most common, and when operated
at the proper flow rate for the size of filter,
they convert the ammonia and trap fine
particles for water clarity. Aerated biofiltration
does a huge volume of ammonia
conversion because of the high dissolved
oxygen content but won’t trap fine particles
for water clarity. The caution here is that
aerated biofilters have a much higher flow
rate but must be used in conjunction with a
fines trapping filter or excellent pre-filtration
in order to maintain good water clarity.

The majority of biofilter manufacturers
overrate their equipment or use
a “once every two hour” turnover rate
calculation in their marketing. Unlike
water gardens, however, koi ponds
generally need to have a turnover rate
of at least once an hour. Turnover rate
is defined as the number of times the
total volume of pond water is sent
through filtration and back to the
pond in one hour. When choosing a
biofilter, make sure you’re applying
the right flow rate to the right piece
of equipment for a given situation. A
good example is the pressurized filter
market. If a specific manufacturer
states a capacity enough for a 10,000-
gallon pond, that’s usually at a two-hour
turnover rate. That means that at
a one-hour or 45-minute turnover rate,
it should flow between 3,500 and 5,000
gallons per hour at a maximum.

Oxygenation

Good circulation and high dissolved
oxygen content are important, so try not
to create shapes in the pond construction
that trap debris, and install current
jets where necessary to promote good
flow characteristics. Install air diffusers
on timers, and don’t think that a waterfall
is always going to be enough oxygen for
the pond. Both koi and the bacterial colonies
in the biofiltration system consume
a huge amount of the dissolved oxygen,
so add aeration. Run part of the system
with air-lifts whenever possible. Air-lift
pumping systems move the water and
add air with the same energy, keeping
the pond consistently oxygenated in real
time. Open biofiltration exposes more
of the pond’s surface area to oxygen,
while pressurized filters consume oxygen
without adding any.

Koi can grow to be quite large. Some of these koi are over three feet long!
Koi can grow to be quite large. Some of these koi are over three feet long!

Food

Feed a high-quality food with a high
natural protein content derived from a
source the fish might actually have access
to. I feed a 49 percent protein food with
no fillers. This keeps my koi and my
biofilters healthier. A koi’s natural diet
does not include wheat germ, chicken
feather meal, soy, corn or algae. Koi do eat worms, rotifers, mollusks
and the critters that live in
the algae you think they are
eating. All of these have a
protein content of over 50
percent, and koi graze all
the time.

On a final note, a koi’s
head should not be the
widest part of its body. A
healthy koi will expand out
behind the gill plates and
have a nice, curved body
shape. Follow the requirements
I’ve outlined above,
and soon all of your koi will
start showing some healthy
curves!

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