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post #1 of 9 (permalink) Old 11-08-2007, 04:45 PM Thread Starter
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long flat tank building

sorry for not doing a search but my net connection is poor right now.
I want to build a low wide tank for loaches. It will have a strong cross like a stream current with "dead pools" etc.
so I go on garf and the tank calculator tells me I only need 1/4" glass!
this is only going to be 16 tall x 24 back and at least 7 feet long.
Is the garf calculator is tricked by this tank only being 16" high?
I did do a search for building a tank like htis and couldn't find anything like it except huge tanks.
thanks
ps- any tank building links that I might have missed are always welcome.
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post #2 of 9 (permalink) Old 11-08-2007, 04:58 PM
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The thickness of the glass is dependent on how high the tank is. Water pressure only increases with depth. 1" of water in a 75 gallon aquarium has the same amount of pressure on the glass as 1" water in a 2.5 gallon aquarium. The reason the glass is thicker on the 75g is because put 20" of water in it compared to the 8" you can put in the 2.5g.
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post #3 of 9 (permalink) Old 11-08-2007, 05:51 PM
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That doesn't sound right. You would have to consider the total volume of water vs the amount of glass. Of course I could be totally wrong but it seems to me that 1000 cubic inches of water pressing on 100 square inches of glass will yield more pressure than 1000 cubic inches of water pressing on 250 square inches of glass.
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post #4 of 9 (permalink) Old 11-08-2007, 05:58 PM
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I wouldn't build it with 1/4 glass. the problem is that it is too long. even though the glass won't have very much pressure on it at any one point the force of adding up that pressure over the whole 7' (about 370lb if my calculations are right) will cause it bow, and my guess is that it will bow too much with 1/4. you would either need to have a couple cross braces/euro brace or use thicker glass. the cross braces or euro braces are probably your best bet, but i still would go with a little thicker glass just for a bigger safety factor. that tank will be about 150 gallons and that is a lot of water which you don't want ending up on your floor.
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post #5 of 9 (permalink) Old 11-08-2007, 06:17 PM
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newshound, just a tangent suggestion about your shallow tank plan.

- make sure you decide if you will primarily view this tank while sitting
or while standing. a shallow tank really needs the cabinet height to be
much closer to eye level than a deeper tank.

- a very nice idea when doing a shallow tank is to use pendent fixtures
so you can grow lot's of emerging stem and flowering plants. that way
you can enjoy the top of the tank, as much as the midwater.

pendent fixtures, especially Metal Halide, will throw wonderful shadows
toward your tank bottom especially with that strong water flow plan.


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post #6 of 9 (permalink) Old 11-08-2007, 06:54 PM
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the calculator is returning that number because the design is so shallow. you could build a tank as big as a lake and the amount of water pressure against the glass would keep the same relationship to depth.

still, you should use thicker glass. a tank that size will be much more subject to forces such as bumps and even wave splash than a smaller one.

you'll also want to make sure you have a perfectly level surface for it, especially with the 7' length.
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post #7 of 9 (permalink) Old 11-08-2007, 07:04 PM
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Quote:
Originally Posted by puchisapo View Post
the calculator is returning that number because the design is so shallow. you could build a tank as big as a lake and the amount of water pressure against the glass would keep the same relationship to depth.
although your statement is true, pressure isn't everything. Even though the pressure with respect to depth would be the same the force on glass won't be the same for shorter tanks as it will be for longer tanks. And force is what causes problems not pressure. My guess is that the calculator is assuming that you are going to build a tank with standard dimensions, not one that is 16 in tall 7 foot long
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post #8 of 9 (permalink) Old 11-08-2007, 07:34 PM
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The GARF Tank Design calc includes top and side braces. The braces will keep the glass from bowing. So the only thing that dicates the glass thickness is how much pressure it can hold.

You guys are right that the total force on the glass increases with length. Which would increase the deflection of the glass. But that has been taken out of the equation by including the side brances.
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post #9 of 9 (permalink) Old 11-08-2007, 11:07 PM Thread Starter
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thanks folks
I figured thicker glass that is for sure.
more later (at work ;-)
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