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Old 10-04-2004, 11:22 PM   #1
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want to build a big tank but have a stupid question

ok, I want to build a tank roughly 8 feet wide 4 feet deep and about 2 feet thick. To make a long story short, use a 4x8 sheet of acrylic for the viewing window. I have an above ground pool and it is 4 feet deep in the shallow end and the metal surround of it is literally as thin as a japanese car fender. I am having a really hard time grasping how an aquarium needs thicker than 1/2 for this project when my pool being 18x36 is literally about 20,000 gallons not 300. Anyone want to try to tackle this one for me? It seems to me that I could literally make an aquarium out of 1/8 aluminum and put a rubber tarp in it and it would be way more solid than the pool.

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Old 10-05-2004, 05:32 PM   #2
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To clarify, we use the dimensions of length, width, and height. Eight feet long, two feet wide, and four feet deep. ~ 450-500 gallons. That's a BIG TANK! I cant tell you right now the acrylic window will need to be stupid thick and stupid expensive. You're looking at lan inch thick, maybe even an inch and a half.

As for the rest of the tank, 1/2" and 3/4" plywood is just the standard. I used 3/4" on my 85gal and it it far more strength than needed. If you're pool is like most other above-grounds I have seen, it has braces/columns supporting the inner metal surround. That's why you can use a thin metal on such a large container. If there were no braces around the perimeter of the tank, the thin metal would not be able to hold it's shape and eventually begin to bow out, possibly even fail at a seam. With a DIY tank this big, it is best to overengineer things. We don't want to tempt fate with the lives of our fish and the wellbeing of our houses with that much water! 3/4" ply would be ok for the walls, but some additional bracing wouldn't hurt.

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Old 10-05-2004, 11:52 PM   #3
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So why would the plexi need to be so much thicker than plywood? Plexi should be more solid than wood. I see car speaker boxes with plexi that isn't very thick that sustain far more abuse than an aquarium would give, however, they aren't 4x8 either...lol.
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Old 10-05-2004, 11:54 PM   #4
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if it dropped to 3 feet tall, how thick would the plexi need to be?
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Old 10-06-2004, 01:43 AM   #5
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Hak, you can't compare a above ground swimming pool with a fish tank. The pools are tested as mentioned above with the supporting structure and will work as long as they are installed properly. I've seen pools blow out after heavy rains when the stakes, supports give. I would advise designing a tank with a little overkill structurally if possible.
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Old 11-08-2004, 02:46 PM   #6
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I agree it would suck to have 500 gallons of water spill out into your living room.

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Old 11-08-2004, 10:58 PM   #7
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I have never built anything that big ... but I've seen one like that at the local Big Al's. It's about 4 feet tall & about 8 to 10 feet wide & maybe 6-8 feet deep & supposed to be 10,000 [Edit : That's liters . not gals ... sorry .... works out to 2000+ gal]

Anyway, they use acrylic that looks to be 1 inch thick, with thick band of bracing around the top rim, and all the joints & corners are braced as well. The whole thing is set in concrete & they might have some hidden embedded bracing as well.

Yes, acrylic is stronger than plywood .... and I would be a bit leary using 3/4" plywood for a tank that big without bracing all the joints .... the garf butt joints with screws is prob not strong enough <I won't use joints like that for my furniture - they won't last - but furniture is subjected to much more stress as the load is not evenly distributed like a tank of water is....> With that much water, I would certainly overkill & brace all corners & seams with extra lumber, and prob every couple feet along the length ..... Come to think of it, I would prob not use plywood at all ... but concrete - basically build an indoor pond with an acrylic window.
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Old 11-10-2004, 02:43 PM   #8
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I would agree with jsoong on the concrete suggestion. This will save you a fair amount of cash as well.

The biggest reason an acrylic tank needs such thick material is exactly as pointed out above, a pool is supported heavily along the perimeter. There are a few other reasons to. Aluminum and rubber are quite flexible while maintaing a greater strength than acrylic. They will give and flex with the movements of the pool and rebound. Acrylic is not as flexible and easily cracks if flexed under a load. But, obviously you wouldn't like using aluminum and rubber for an aquarium, unless you dont mind not actually being able to see your fish

So again, I'll second soong's advice and for a tank that large, contruct a cement encasement and leave room for a 4x8x1" sheet of acrylic on the viewing side.

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