A Glass Block Koi Pond / Fountain

This site describes a pond constructed with glass block. The water is held
in a liner supported by a metal frame. The glass block facade is back-lit
and does not actually contain the water. The following text and images
explain the construction.

Goals & Design Constraints:
In The Beginning...
The site, before.

Ivy, old planter, etc., cleared away.
Site preparation begins July 2001.

Equipment pit is behind the pond.
Digging the equipment pit.

The equipment is installed in a brick-lined pit behind the pond.
The pit is 4' deep and is comprised of three levels. The lowest level
holds the biofilter and has a 3" drain at the bottom. The pump and leaf
basket are bolted on the middle level slab.

Plumbing rough-in.
Laying out the plumbing.

rebar in bottom of equipment pit.
Bottom of pit has 3" drain. Never pour cement without Rebar!

Dad's in the pit.
Pit almost swallows Dad.

Philosophy: If you can afford it - install only the best, and
oversize it. The result will be lower maintenance, longer life, fewer
troubles, more time to enjoy the pond. Consider it an investment that
will pay off over time. (Save money by doing the labor yourself.)

Completed equipment pit.
Completed equipment pit.

Ready to pour the glass block footing.
Ready to pour glass block footing. Background: Pacific & Channel Islands

Footing is not large, but contains 4 runs of rebar.
Four runs rebar in footing.

A second pour of white cement finishes glass block footing.
White concrete caps the footing.

Laying glass block - not for the timid!
Laying glass block - not for the timid!

Glass Block completed.
Glass Block completed..

Pond Lighting

The glass block wall is backlit using rope light and reflectors.
The rope light is 110V, clear, and in a continuous length (~50 feet).
The U.S. made rope light, and its power cord, are UL approved. This is
especially desirable as this pond was permitted and had to pass electrical
inspection. (Everyone who got a permit for their pond raise their hand!)

If you have ever sold a house you may have found out that un-permitted
work 'comes home to roost' at the worst possible time. Even a missing
switch plate can stop a VA loan. Before I got the permit and began work
I had the building inspector come out and visit the site. This provides
an opportunity to ask questions, and to show the inspector that you care
about the process and about doing a good job. You want to have a good
relationship with him or her. They make the rules. It's not like you
can go to their competitor if you don't get along with them!

The rope light is held in a 1/2" aluminum angle that is attached to the
top inside edge of the glass block. 4-40 stainless studs were set in the
mortar to fasten the angle into place and to pinch-hold the rope light
into the angle. The aluminum angle was bent to fit the curve of the
glass block wall using a homebrew die in a milling machine vise. Holes
for the studs were punched with a Roper-Whitney punch.

4-40 SS studs set in top course.
Studs will hold rope light..

Rope light held in aluminum angle reflector.
Rope light in place.

Rebar stakes being installed.
Rebar stakes being installed.

Liner Support

The liner is held inside of essentially what is a giant metal bowl.
The primary reason for this, or at least for the metal floor of the
bowl, is that this here is gopher country. They'd chew
through the liner in short order. The walls of the bowl also support
the liner and result in a several inch gap between the water containment
and the glass block. This gap is where the rope light is, as well as
the reflectors that back-light the glass block. Of course, it would be
neat if the water containment walls were actually the glass block
itself, but if that were the case one would spend the rest of ones
life trying to clean the algae off of the glass. The metal bowl acts
somewhat as a secondary containment system for the water, but is not
tested to be water tight.

Construction of the metal bowl begins by grinding the ribs off of one
inch of one end of each of 71 3-1/2' long 1/2" rebar stakes. These are
driven 18" into the ground in a 15' diameter circle within the glass
block wall - de-ribbed ends up.

A "story" pole is employed to keep the diameter in check. This 3/4"
EMT story pole was used throughout the project to meter diameters and
check levelness. The 2" fountain feed at the center of the pond was
the datum point from which all was measured. This pipe was roughed-in
just above ground level then fitted with a PVC pipe cap with a 1/4-20
stud set in the center. A Minerallac strap on the end of the pole
mated to the stud. Various widgets were fitted on the other end of the
pole to assist construction: to keep the glass block wall the right
diameter, to keep the rebar stake spacing in line, etc.

The rim of the bowl is a circle of 1" EMT. Approximately 5 ten foot
lengths of 1" EMT were bent in a curve to match that of the rebar stake
circle. This was one of those tasks that turned out easier than
expected. After the EMT was bent it was drilled through one wall with
a 1/2" diameter center bit, every 8". The de-ribbed ends of the rebar
stakes fit into these holes. Internal couplings were fashioned to
connect the rim segments. This rim makes the rebar stake ring
extremely rigid. The liner will be folded over the EMT rim to retain it.

The side of the bowl is a strip of galvanized sheet metal attached to
the inside of the rebar stake circle using Liquid Nails Heavy-Duty
Construction & Remodeling adhesive. This stuff is waterproof,
weatherproof, and extremely strong. The same adhesive is used to join
all of the sheet metal sheets used to form the bowl.

Sheet metal band being attached to rebar stakes..
Sheet metal band installation.

EMT being fitted on ends of rebar stakes.
EMT fits over ends of rebar.

Island and its base at pond center..
Island and its base.

The Island

The island is one of those giant plastic flower pots turned upside-down.
It's about 2' tall, 2' in diameter at the opening (now the bottom), and
19" in diameter at the bottom (now the top of the island.) It sticks
above the surface of the pond by about an inch. The 2" pond water feed
is co-axial to the island and has a bulkhead fitting to pierce the
liner - which is draped over the island. So - the flower pot itself is
actually under the liner, thus has no tendency to float. The pot is
reinforced inside against side forces collapsing it. A concrete base
was poured for the pot, and dish-shaped with a drain near the center
just in case the bulkhead fitting leaks. This island drain empties to
the drain at the bottom of the equipment pit so the soil under the pond
doesn't get soaked. Along with the 2" water feed in the island are
several spare conduits for water, electrical, and whatever. It is not
anticipated that these will be needed, but if they are the top of the
island could be cut through to access them. The island is topped by a
glass disk, 3/8" thick 30" diameter with a 6" hole cut through the
center. This was fabricated by a local glass shop. I etched and
painted black the bottom of the disk so the inevitable algae wouldn't
show through. It gives a nice finished look to the island & fountain.

Polyethylene sheet is laid down, then forming the metal bowl begins.
Forming the metal bowl.

Bowl done.
Finished metal bowl.

Liner is installed.
Liner is installed.

Pond Lighting, continued...

The light from the rope light bounces off of reflectors positioned in
gap between the liner bowl and the inside of the glass block wall.
These reflectors are cocked so as to fairly evenly back-light the glass
block. They galvanized sheet metal 2' tall and 3' wide. The top of
each reflector leans against the EMT rim of the liner bowl, the bottom
rests at the base of the glass block. The bottom edges are trimmed
slightly with a tin snips so the reflectors lie in a curve that closely
matches the round pond. The reflectors are not otherwise fastened in
place so that they may easily be replaced. They are covered with
Reynolds Wrap Dazzle Holographic Aluminum Foil which adds just a touch
sparkle to the light seen from the pond wall, day and night. This foil
is available at grocery stores and is attached with spray adhesive.

Another Reynolds product adds a touch of color to the back-lit glass at
night. The rope light is wrapped with Reynolds Plastic Wrap, mostly
the blue tinted with occasional sprinkles of violet.

Holographic foil adds daytime color.
Holographic foil adds daytime color.

Tinted plastic wrap plus holographic foil add night color.
Tinted plastic wrap plus holographic foil add night color.

The fountain outlet in the center of the island is lit from within.
The water flows through 2" bulkhead in the center of the island and out
a 6" section of clear 2" PVC. I fabricated a light and threaded it
through the 2" line from the equipment pit, holding the light bulb at
the bulkhead fitting so the light bulb is not directly visible - only its
light. The bulb is a small bi-pin 12V 100W quartz halogen (type FCR).
Its pins are soldered to a length of underwater-rated type SOOW power
cord. That connection is potted with UV-6800, an underwater rated
sealant. The bulb, and the potted connection, are covered with a
special Teflon heatshrink tube. This assembly is threaded though a
waterproof cord grip and a 2" tee fitting just before the filtered
water exits the equipment pit. The light is operated at 25 Watts
half-wave DC via a diode and a 35 Amp 13VAC transformer. It's really
quite bright. (FWIW: I am an electronics engineer and a licensed electrician.)

Light reflector positioned between liner bowl and glass block.
Light reflector.

Light rope is wrapped in colored food wrap..
Light rope wrapped w/colored food wrap..

Fountain light is threaded through this tee.
Fountain light power passes thru Tee.

Underwater Lighting...

I built seven underwater fixtures that encircle the pond. They are
hooked over the liner and are positioned just a couple inches under the
water level. Angle-aluminum reflectors keep one from seeing the glare
of the bulbs. The effect is that the entire contents of the pond are
illuminated. The bulbs are 50W 12V quartz run at 6V and are packaged
similarly to the center fountain light.
Underwater light.
Underwater light.

View from above at night.
View from above at night.

Capping the Gap...

The gap between the liner and the glass block is covered with
curves sections of lightweight concrete - like a bench seat.
I cast them using a mix of white portland cement, plaster sand, and
pumice. 3' sections weigh about 60lbs and are easily removable.
One side of each section rests on the top of the glass block.
The inner sides rest on the rim of liner bowl.
The rim of the liner bowl is 1" EMT over which is laid
two layers of polyethylene sheet, then the liner, then a cap made from
slitting a 47' length of 1" black vinyl tubing. This vinyl tubing
'snaps' over the rim covering and protecting the liner edge.

Mold for cap sections.
Mold for cap sections.

Misc photos...

Pit full of equipment.
Equipment pit.

Tinted Lexan cover protects equipment pit.
Tinted Lexan cover protects equipment pit.

Aqua UV Giant Leaf Basket
Giant leaf basket.

Water lilies were potted in broad 5-gallon pots in aquatic plant soil
in hopes of keeping the water clear. Aquatic soil was topped by a layer
of washed river rock. aKwatik Lily Feeders were placed in each pot.
Pots drop into PVC pipe stands fashioned to position pots level and at
the correct depth. These stands will be shortened as the lilies grow.
A feeding ring was made from a scrap of drip line and a drip line coupling.

PVC pipe stands were made to hold the water lily pots level and at the correct depth.
PVC pipe stands hold water lilies at right depth.

Pot at right depth.
Pot at right depth.

The Livestock...

I wasn't sure what kind of fish I wanted in this new pond. I don't
find the thought of getting deep into the Koi culture all that
appealing, i.e.: learning all of the classifications. It just doesn't
interest me. I especially wanted to avoid having animals that had been
bred for hundreds of years just for certain patterns of colors on their
backs - you have to give something up when you do that - like disease
resistance. A fellow ponder who I had consulted with on my plumbing
design told me about the drawer full of medicines he had for his Koi
and the hassle of keeping them healthy. He recommended goldfish, which
made a lot of sense. Then I came across Butterfly Koi and this
statement on the breeder's web site (Blue Ridge Koi):
"Due to their hybrid vigor they are stronger, more hardy, and more
disease resistant than either common goldfish or regular koi."
And, they're quite pretty. I'm sold! I've decided to make this
exclusively a Butterfly Koi pond. It should be said that this pond is
definitely not a purist Koi pond - its depth is marginal for Koi and it
contains plants, which are usually absent in serious Koi ponds.
So far all of the little guys have been purchased from FINS, a clean
and friendly pond & aquaria store in Camarillo California.
FINS Aquarium & Pond Specialists
2175 Pickwick Drive, Camarillo CA 93010, 805-389-1128

The Drain...

The pond has a semi-bottom drain. Because the pond location cannot
tolerate leaks I did not want to risk a conventional bottom drain.
Repair of such a drain would require tearing up the pond. I opted for
what I call a semi-bottom drain. A 2" ABS pipe circles the bottom of
the pond just inside of the outer perimeter. A 3" bulkhead pierces the
liner about a foot up from the pond floor. This 3" makes a sharp 90
down into the pond to tee into the 2" ABS circle. On the "dry" side of
the liner the 3" makes another sharp 90 down into the ground and makes
its way into the equipment pit and a 3" knife valve. Back inside of
the pond every couple inches a hole is drilled in the 2" pipe circling
the bottom. The third of the circle farthest from the exit bulkhead
has a 1/2" dia hold drilled in it every 2". The third of the 2" pipe
nearest to the bulkhead exit has 1/4" holes every 2". The remainder has
3/8" holes. This is an attempt to draw water into the drain equally
all around the diameter of the pond. There are no stagnant corners for
ammonia or toxins to linger. Another detail - the sharp 3" 90's are
actually 3" ABS Tee fittings as they are more compact that regular 90-
degree fittings. One leg of the tee that is inside of the pond (the
tee that connects to the drain encircling the pond) points up toward the
pond surface. This tee is reduced to 1/2" and stops a few inches below
the water line. This open 1/2" port should act as a siphon breaker if
something breaks in the below-water-level equipment pit resulting in no
more that half the pond water siphoning, or being pumped, out.

Plumbing Diagram


One issue of above-ground ponds is the loss of the insulation value of
the soil that would have formed the sides of the water vessel. The
Pittsburgh Corning Premiere Series block used for this pond has an
R-value of 1.96. This, in addition to the 8" air gap between the glass
block and the water vessel, are probably roughly comparable to an
in-ground pond. Fortunately, at this location it never gets cold
enough to freeze anything more than a thin film of dew, and even that
occurrence would make the news. For more information on the glass
block used visit:
Pittsburgh Corning Corporation, http://www.pittsburghcorning.com

Status... (December 28, 2002)

The pond has been wet for five months now. Here are some observations:

The water has never been anything other than crystal-clear. I chalk
this up to:
1) The more than ample UV light.
2) The fact that the water lilies are potted in aquatic soil, not dirt.
(If you don't want dirt in your pond, then don't put dirt in it!)
3) Everything that's gone into the pond has been washed and sterilized.
4) The pond is only 5 months old.

The Aqua Ultraviolet Ultra Leaf Basket has been a real winner.
It doesn't need cleaning even weekly, and it could probably go a month.
The Aqua Ultraviolet Ultima II 5.0 biofilter has also worked out well.
So far it needs only one minute of backwash and one minute of rinse
once a week.

One of the last things I did was to build the underwater lights.
They contribute a lot to the pond. Everything in the pond is visible
at night instead of it looking like a black pit.

The plants have not done well. I believe this is due to several reasons:
1) The late start (September/October) in planting.
2) The water lilies got caught for a week in Ag inspection between
the supplier in Colorado and here, which didn't help their health.
3) The pond is too clean and devoid of nutrients.
4) The city water is extremely alkaline (high KH and pH).
5) Microscopic larvae have attacked some plants.
Now that I recognize these problems (3-5) I am working on solutions.
I'm adding potash (potassium), aquatic plant stimulant (trace elements),
Koi Clay, and Dipel biological control for the larvae.

The equipment pit has a serious condensation problem when its cover
is in place. Moisture condenses on the plumbing and the bottom of the
Lexan cover resulting in rain inside of the pit. I'm working on
elevating the cover slightly to provide some ventilation.

Status... (May 21, 2003)
Still never any 'pea soup' algae, but string algae has been a problem.
Lost one Koi to a Heron. Scarecrow sprinkler now installed.
Only once measured a trace of ammonia since the pond was built.
So far no problems at all with plumbing, biofilter, UV, pump, etc.

Status... (August 1, 2003)
Pond one year old today.
Discarded the Akwatik fertilizers. They constantly clog with fertilizer
tabs. They are not large enough in diameter - especially at the elbow.
Better off to make one's own with larger diameter pipe which should be
large enough for two tabs to lie side-by-side.
Not able to get Water Hyacinths to survive more than a month or two.
I've tried adding potash, iron, Epsom salts, aquatic stimulant - they
still die.

Status (6/05)... Okay, now it's fashionable to call this a Blog!

Status (9/06)...

Status (10/06)...

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email: s t e v e @ k i s s i n g f r o g s . t v

(C) 2004-2019 Steve J. Noll

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