Feeder Fish
MFK Member
Feb 23, 2005

In the beginning the big question was, should the monster tropical fish aquarium be constructed out of plywood or cement? Ted voted for wood as he had finished his 2400 gallon plywood fish tank several years ago and it has been a great success. Carl would like to have gone with Acrylic but for an aquarium 16 feet long the cost of custom Acrylic sheets over 8 feet in length is prohibitive. Todd wanted to build his aquarium using cement. A business associate in the concrete forms and foundations business was ready to start yesterday.

Concrete was Todd’s choice for the new 2500 gallon aquarium; it just had to be 100 gallons larger than Ted’s 2400 gallon plywood fish tank. The engineering was next, for the aquarium construction project to be located in the basement of Todd’s house. The design called for walls 6” thick reinforced with 5/8” rebar running along the bottom, center and top and wired to the vertical rods on 18” centers. The 6” thick concrete walls cover all the reinforcing rods. The concrete wall thickness and size of rebar may have been slightly over engineered but as we began thinking about the Seattle Fault it seemed wiser to over engineer.

Carl and Todd are looking over the site for the 2500 gallon concrete tropical fish aquarium in Todd’s basement on March 7, 2005. A near perfect concrete foundation for the aquarium came with the house; a slight modification added extra width to the aquarium. Notice the wooden shelf extension. Todd began clearing the area in early March 2005; the black ABS sewage drain pipes could not be moved. The laminated overhead beam limited the height of the concrete aquarium. The 160 gallon Plexiglas aquarium on the floor with the blue background will become the sump and housing for the bio tower filter.

All construction materials must be carried down a narrow flight of steps and through this basement door. We got in the habit of singing out a warning before making the turn with an armload of lumber.

On Friday March 11, 2005 the concrete contractor started building the forms and shaping the 5/8” rebar into place for the concrete aquarium. The final overall size of the concrete sting ray aquarium tank is approximately 17 feet long by 6.5 feet wide by 4.5 feet high.

Construction of the forms continued throughout the day. Notice one of six white PVC 1” aquarium water return pipes is set in place to be sealed in the concrete back wall. Notice the blue shoulders on the snap ties; once the cement has hardened into concrete the wire ties holding the forms together can be snapped off and concealed.

There are three 2” diameter pipes placed in the back wall to carry the aquarium overflow water back to the 160 gallon sump. The placement of these pipes is important as the water level will be maintained in the aquarium by adjusting the height of these pipes. Note the 1” holes drilled in the back wall for the water pipes which return filtered water from the sump to the 2500 gallon aquarium. The position of return water pipes is important as they will keep the aquarium water in motion; eventually the fish waste will be filtered out rather than accumulate on the bottom.

Constructing the support forms above the open expanse of the window can be tricky. If you are good enough you can do it with your eyes closed.

Although this is not a government job site, some construction work requires 3 supervisors for each person actually building the aquarium. The crew worked most of Saturday March 12, 2005 and completed the forms and positioning of the 5/8” reinforcing rods by the end of the day Monday March 14, 2005, in all, just 3 days time.

Todd and I are in the Home Depot tool rental department to pick up two cement mixers. As usual, Todd is consulting over the phone helping a customer solve a computer problem.

White Cap Contractors Supply delivers 200, sixty pound bags of “pre-mix” right to Todd’s front door.

Oops! The loader can’t get close enough to the bank to put the pallet load of cement in Todd’s yard; we will have to carry it up from the street.

We pull the crew away from the forms work to help us get the bags of ready-to-use cement up the steps and staged by the basement door. Is that Todd carrying cement? Why yes, but we had to take away his cell phone.

With six of us packing cement up the steps, the 200 sacks get moved quickly. Every time I stop to take pictures someone has to double up and carry two bags at a time.

We are all glad the cement moving job is finished; 45 minutes must be some kind of record.

The construction crew takes a break; then it is back to finishing the forms. It is still Monday March 14, 2005 and we will be ready to pour cement tomorrow.

This is the cement type we used. There are many kinds of ready-to-use cement, some fast drying, others with fiber threads; it is important to research and select the proper cement for your application.

We get an early start Tuesday morning March 15, 2005 setting up two Home Depot rental cement mixers; the pour must be continuous and we will not go home until all the cement work is finished.

In a few minutes we have it down to a system; two 60# bags of “ready-mix” in the hopper will create one cubic foot of cement in five minutes. All six of us have a job; mixing, carrying and pouring cement into the aquarium forms is non stop work.

We try to have a batch of cement ready every three minutes; this is about all the bucket brigade can handle. At times we get a shout from the basement, “Too dry!” and sometimes “Too wet, cut back on the water!” The mix must be just the right consistency.

As the day progresses some of us can trade our routine with others, otherwise the same people do all the carrying of the 5-gallon buckets which is the hardest work.

The electric concrete vibrator is used to work out air bubbles and ensure a uniform distribution of the concrete settling into the forms...

There is very little overhead clearance when pouring cement from the heavy 5-gallon buckets into the top of the forms.

Pouring cement for the aquarium walls and floor must be continuous. As the form walls fill with concrete, the weight of the material pushes out the bottom of the form through the opening where it will join with the floor. The material must be contained in some way temporarily while the floor is poured. Competent concrete contractors know all the tricks for this kind of pour. If the floor was to be poured on another day there would likely be seepage at the intersection between the walls and the floor. Notice the wire mesh in the floor of the concrete aquarium tank.

The fresh cement floor must be trowel led as smooth as possible. If the aggregate is too wet water forms at the surface which might cause the cement to develop surface cracks as it dries.

There it is all tucked away in Todd’s basement; an aquarium built exclusively for fresh water Sting Rays. It is 5 pm Tuesday March 15, 2005 and we are headed home after a long exhausting day.

Three days later on Friday March 18, 2005 the forms are removed, somewhat reluctantly at times. Removing concrete forms takes a lot longer than you might expect.

Bending the snap-tie rod causes it to break at the predetermined weak point recessed in the concrete located just behind the blue plug.

It takes a bit of skill to cleanly snap off the tie rod which held the forms together. A short section of the snap-tie rod remains in the concrete; the holes are plugged with fresh cement. Any possible leaking along the snap-tie rod will be eliminated when the Epoxy paint is applied to the inside of the aquarium. .

The 12” wide center column must be well reinforced as it will support both 30” high aquarium windows.

The weight of the water along the 17’ aquarium wall is supported with a built in concrete strap across the top to prevent a possible blow out.

Each aquarium window is 6’ wide; the supporting concrete walls are 6” thick throughout.

The concrete aquarium window viewing area is 30” high.

The concrete forms removal and cleanup is almost complete Friday March 18, 2005. There is a bit of cosmetic touch-up work yet to do on the outside surfaces of the cement aquarium.

When the concrete forms have been removed from your aquarium your yard may look something like this. It is hard to visualize how all that material could have been used in such a small space.

On March 18, 2005, Todd’s 2500 gallon concrete aquarium is nearing completion. Will the fish tank windows be glass or plastic? Todd may also be thinking;

“Will the cement aquarium hold water?” Up to now this concrete fish tank project in Todd’s basement has moved along swiftly with virtually no hiccups. The aquarium site prep work took several days. The forms to contain the cement were erected in three working days. The cement was poured in one day. Now it is “wait a while time” for the cement to cure so the Epoxy paint / concrete sealer, can be applied.

Two months later on May 17, 2005, Todd’s 2500 gallon cement tank has cured and has been painted with dark blue non-toxic Epoxy concrete sealer paint obtained from Aquatic Eco-Systems; Three 2” diameter overflow drains and the six 1” diameter water return pipes are all plumbed in. Todd decided on ¾” Lucite for his aquarium windows which will be sealed with GE Silicone II.

The aquarium window gasket seal between the concrete and the Acrylic is GE Silicone II available at Home Depot, generally costing under $5.00 a cartridge. Although the Silicone does not bond firmly with the Acrylic it makes a very good seal such that the windows will not fall inward when the water is drained out of the aquarium. The contact area between the Lucite window and the concrete is 1-1/2”; a 2” contact area would have been better. We used about 14 tubes of GE Silicone II per window; the bead was extra thick to ensure all nooks and crannies would be filled and sealed tight. For many years we have been using GE Silicone I and recently GE Silicone II which is labeled “Kitchen and Bath”. This product appears to be pure Silicone and once cured has never been any problem for our aquarium fish. Lately some of the GE Silicone II products have something new added to their labels: “Bio Seal Mildew and Mold Protection” and or other similar wording. At this time we are purchasing only Silicone II without the “anti-mildew” label as we have no experience with the potential toxicity in using the newly labeled product. In the picture the tube on the left has the “Bio Seal” label which we advise not using until more information is available. The two GE Silicone products on the right hand side of the photo appear to be unchanged and exactly the same material which we have used in past monster aquarium projects.

Lifting the ¾” Acrylic panel into its recess in the concrete aquarium frame is a delicate maneuver. We had wood timber bracing with protective towels ready to wedge into place between the Lucite window panel and the back wall of the aquarium. We imbedded small shims in the Silicone II bead around all sides of the window, spaced every 4” or so. The ½” by ½” by ¼ “ thick plastic square shims were cut and made ready for this application to prevent the water pressure from squeezing the silicone out of the seam over time. In the past we have used neoprene rubber shims of a similar size which I think work better than the plastic.

The first window is seated in place; notice the triangular braces and the woodworking clamps overhead used to hold the window securely while the silicone cures. You will need lots of paper towels and if you get Silicone on your “old” clothing, remove it as soon as possible. Pharmacy alcohol, 90% or better is adequate for silicone cleanup.

It is Tuesday, May 17, 2005 9:08 in the evening and both windows are in place and braced. Two of us might have done the job but I advise anyone sealing windows as we did to have at least 4 people on hand. There is always a need for someone to press more Silicone into a gap which did not quite fill or position a clamp while the window is held in its frame. It looks messy now but cleanup is relatively easy when the silicone cures.

The Silicone sealing the aquarium windows is quite thick in places and although the label indicates that it can cure in 24-48 hours we know better. During the week allotted for the Silicone to cure I delivered one ton – forty 50-lb. sacks of Monterey sand to Todd.

“I’m busy Ted” said Todd, “Would you please just stack it by the basement door.” It took me two hours to move the forty bags of aquarium sand up the stairs to the doorway.

A few days later I said “Sorry Todd, I am busy this week, I hope you get the sand washed by the time you are ready to fill the tank.” Todd washed all the sand himself, so he said, and called to say the aquarium was full of water. I had to see this and rushed over to Todd’s house in Seattle. The aquarium water was a brown mess.

“I washed it before I put it into the tank, really I did!”

“Really? Just because the dealer said “pre-washed” doesn’t mean it is ready to go into the fish tank. Todd.”

It took several days and frequent cleaning of the fiber filter pads before the aquarium water cleared up. Chunks of wood and other debris were filtered out in the fiber padded tray.

The 160 gallon plastic aquarium was modified into a sump and housing for the bio tower. The main pump, a Performance Pro, 1/4 HP, 2.5 Amp model circulates close to 4,000 gallons per hour through the 2500 gallon aquarium. There are three 2" diameter pipe overflows feeding the sump and six 1" return pipes pushing water back in to the concrete aquarium. The total cost was about $8,500 US, including pump filter, Lucite windows, all concrete construction materials, labor, lights, covers and sand.

You might be wondering why Todd went to all the trouble and expense to built this monster concrete aquarium in his basement. The two photos following will show you why. Todd’s Sting Rays have been living and getting larger in 300 gallon Rubber Maid tubs. If he wants to visit his Sting Ray friends, he must open the lid and view them from overhead.

Todd is talking to his Sting Rays in their former Rubber Maid stock tank home.

Finally on June 1st 2005, Todd’s new 2500 gallon concrete aquarium has clear water and fish!

The following photos include some of Todd’s Sting Ray collection, taken on or about June 1, 2005. The Sting Rays and Todd’s monster Silver Arowana love their new 2500 gallon aquarium home in Todd’s basement office, as you can see.

Assorted Sting Rays gathered together in Todd’s 2500 gallon concrete aquarium.

Todd’s hand is dwarfed next to his monster fresh water Sting Ray and this one will continue to grow larger on his mostly shrimp diet.

This fish is a monster fish in his own right and the only exception allowed living with the Sting Rays. This Silver Arowana has been in Todd’s family for many years. Jed, (The TRUST), says it is definitely the largest he has ever seen in person. The fish is about 9” deep and over 3 feet long

It is now April 15, 2006; looking back I realize we had much good fortune in completing this 2500 gallon aquarium. Planning was an important aspect as well as having someone on site at all times who had the experience to keep us on track and not making any costly mistakes. Would we do it differently next time? Not really, although it would have been nice to have a little more head room in the basement.

Disclaimer: Although this concrete aquarium construction project was a complete success; the pictures and text provided here are meant as a general guide only and are offered without any warrantee or guarantee of success. We advise you to hire your own cement contractor and have your concrete aquarium professionally engineered.


Team Rayman
MFK Member
Mar 30, 2005
staten island new york

only on monsterfish keepers
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MFK Member
Jan 27, 2006
Thats a great setup, you have quite a lot of bio-balls. Rays are some of the most beautiful fish.


Fire Eel
MFK Member
Oct 29, 2005
Wow ... that's incredible! :headbang2

I'm planning to do something similar someday (in the not to near future unfortunately).

Thanks for the detailed writeup!:thumbsup:



MFK Member
Mar 30, 2005

10/10 for effort man, that is unreal.

Superb job :thumbsup:


" id rather be a goldfish "
MFK Member
Jun 28, 2005
:drool:... that was alot of work.. but god damn it was definatley worth it in the long run:thumbsup:

del... he said the silver was a lil over 3 ft