Saw something on MFK, somebody built a 45x15x5 koi pond for $6,500. Already a good price, but the one-upper here is that this pond has a 45' acrylic window on it. Here's his breakdown and how he built it, for anyone wondering:
Wood, plywood, screws, etc - $1,000
Acrylic sheets - $2,000
Acrylic glue - $2,000
Rubber liner - $1,000
Stainless steel bolts, DOW 795 sealant, etc - $500
That's the rough estimate for the cost of the lagoon itself - there are other costs not directly associated with the pond, which are below along with a step-by-step of how it was done.
1) Build a 1.5-2.5' deep sand pit on the side of the house (grade slopes away from house, done by hand so no considerable costs added)
2) Use 4x4 posts, roof boards, and shade cloth to build an enclosure around the pit, with a UV-treated tarp on the top and insect netting on the sides (adds a bit to the total cost, but not included since it's not technically part of the pond/lagoon itself)
3) Used pressure treated posts and doubled-up 3/4" plywood to build two 15' side walls (one wall is 50' and it's the side of his house)
After he did that stuff, he built his window (42' long and 43" high) by doing:
1) Joined five acrylic sheets (about 9' by 43" by 3/4") together with four acrylic posts (2' wide and 7' tall, outside of the tank with 1/2 above ground and 1/2 out of ground)
2) Glued another acrylic panel (2' by 43" by 1/2") to each of the four joints on the inside of the tank
3) Glued a 6" wide strip of acrylic (pretty sure 1/2") around the remaining perimeter of each of the five acrylic panes (inside and outside of the tank, top and bottom)
4) Glued two 3" wide acrylic strips along the top, inside and outside of the tank
5) Glued a 6" wide acrylic top along the entire 42' length (so it forms a T-top)
He said that he used about 16 gallons of Weld-On #40 glue, and it ran about $2,200.
After he had the window built, he attached the liner (60' by 20' by 45 mm).
Cross-section of this looks like:
[window][Dow 795][liner][3" wide by 1" thick acrylic strip]
The 3" strip runs the entire length and sides, and is one piece, made out of 1/2" acrylic. It compresses the liner and Dow silicone with 1/4" stainless steel 316 marine grade bolts every 4-1/2", about 100 bolts were used in total.
The vertical sides don't have bolts, but they are screwed to the wooden side posts with 6" by 5/16" screws.
After all that was done, the final steps were:
1) Dress the sand pit by making a 45 degree angle at the window so there's no blind spot below the grade (the window is 43" high, the pond's depth is probably 4-4.5')
2) Lay down the liner underlayment (he used about 4-5 layers of high-quality thick used greenhouse plastic which he got for free from an orchid nursery)
3) Spread the liner out, and do a water test
He said this is as far as he has gotten - he still needs to fix the liner to the top perimeter of the tank, and get some flow going. He's planning on a wet-dry filter running on about 7,000 pot scrubbies, and 40-50K gph of flow spread across 8-10 pumps.
All in all, before filtration he's probably still under $10,000. If this setup works, it would need little modification to house sharks, shape would be an important one and depending on the location it may need to be fully insulated. This pond is in Florida, so he can keep it outside - but for shark keepers, it may be worth it to fully enclose and insulate the pond.
Thought people would get a kick out of it
Oh yeah, here's all of the acrylic he said that he used:
(5x) 9' by 43" by 3/4" - $950 total
(8x) 7' by 5' by 1/2" - $400 total
(5x) 8' by 4' by 1/2" - $600 total
It's all cell-cast and he got all of it from Craigslist, $1,950 for all that acrylic is pretty good.
For reference - I looked into just buying scrap acrylic and melting it down in a pre-made mold of a window, and letting it cool. If I wanted the same volume of acrylic, I would be paying at least $18,000 new. The fact that he got all of that for under $2,000 is pretty incredible.