# Large DIY Glass Aquarium Questions



## Gervahlt (Jun 25, 2009)

Okay, so I'm still in the design phase, but I've run into a few questions and can't seem to find great answers out on the web. I'm hoping some of you can help. I'm working up the design of a 300 gallon tank measuring 96"L x 30"W x 24"H. While researching glass thickness, I used two main sites:

http://www.fnzas.org.nz/index.php?PG=glass1
http://saltaquarium.about.com/od/planas ... ulator.htm

I'm sure most of you are familiar with them. Unfortunately, they're both a bit vague in a couple of places.

1) Doing the calculations from the first site, I ended up with a bottom piece of glass that would need to be 3/4" thick with a deflection of .28mm. Total water pressure will be about 6k N/m2 (5980 to be exact). Do the calculations there figure for tempered glass already since they have different alpha and beta figures for the glass, or can I reduce the thickness back to 1/2" glass by switching it to tempered?

2) According to the article that accompanied the 2nd one, it said that cross-bracing effectively reduced the overall length of the glass you're working with in terms of strength. Following that logic though, I could build a 300 gallon tank with 3/8" glass as long as it didn't exceed 24" in height and was cross-braced every 2'. Somehow, that doesn't sit right with me and I wanted a clarification. Especially after figuring up the more scientific site's calculations where it specifically states that the glass needs to be supported on all four sides in order to work.

3) If you have experience building large, glass aquariums, are there any tips you can offer which will make this easier and less likely to fail? I've done lots of research, but most of what you can find out there seems to have smaller tanks in mind (55g or less).

4) Any suggestions on where to find cheap glass would also be appreciated. This is going to be an expensive project no matter where the glass comes from, but if I can save some $, I'm all for it.

I don't mind putting in the work, and you get experience from each failure, but it can be much cheaper if you can learn from mistakes that other people have made before you make them yourself. The inverse is also true: you can save yourself time, money, and disappointment if you can drawn on the success and knowledge of people who've done it before.

EDIT: I don't want to reduce the safety factor by much from the suggested 3.80 as I have four kids ranging from 18 months to 10 years old. The odds of the tank getting whacked a few times are quite high. *grin*


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## pistolpete (Dec 28, 2009)

have you considered a metal frame tank? this adds a huge safety margin. You could cut your own angle iron and have it welded at a fabricating shop.

I will not venture an opinion on glass thickness, except to say that peace of mind is priceless. You can reduce the stress on the bottom glass by having it supported by the stand. commercially made tanks do this by having a couple of strips of plastic going across the bottom that distribute the load. You can go one better by supporting the entire bottom of the tank evenly with the appropriate thickness of plywood or rigid foam insulation.

Bracing definitely works. the bottom frame is braced by the bottom glass. The top frame should be braced at the very least in the middle, but every two feet is much better. It takes all the stress off the glass. The top braces are placed in tension , but the glass does not have a chance to bow out.


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## Gervahlt (Jun 25, 2009)

I did consider this, and still may go that route, but I took a look today at some manufactured tanks about the same size, but they were about 6" taller. They used 1/2" glass like I'd intended and 3/4" tempered glass on the bottom. Their braces were plastic though and configured in a way that I haven't seen before. It was separate from the trim, which concealed how this was actually put together. Basically though, it was molded 2" wide plastic that looked kind of like a big c-clamp and actually fasted on the outside of the tank with an additional glass knob that it hooked on to (similar to a how old fashioned trunks used to close with that metal latch system).

I have my brother looking at my plans before I begin construction to see if he sees anything wrong. He's a civil engineer and hopefully will spot anything I missed.


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## pistolpete (Dec 28, 2009)

I have frequently used glass strips held in place with silicone to brace tanks. I find this effective, since the glass can be around 4 inches wide, giving lots of bonding area. The danger with glass bracing is that if the glass should accidentally break, a sudden stress on the tank would result.

How will you be making your top trim? Aluminum strips could be screwed to the trim, or even have a channel in the end to slot in on top of the glass.

I have built a couple of tanks using angle iron and found it relatively simple. The only painstaking detail was getting all the solder blobs out of the inside corners. I used a combination of drilling and dremel grinding. Though I have to say that I never attempted anything the size of yours.


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## Gervahlt (Jun 25, 2009)

I wasn't going to have a top trim until reading your post. :?

I had envisioned this as a frameless, all-glass aquarium with glass cross-bracing. I actually like one method of doing this that I've seen before where a 4"-6" long piece of glass is mounted inside the top rim of the tank in a position where you rest the cross-brace on top of it. This allows you to add an additional amount of silicone for the glass to seal to (not just the end of the glass where it abuts the tank wall).

However...now that you mention glass cross-bracing breaking, I can see how that can happen without warning rather quickly. With plastic bracing, you can usually tell when it's getting weak. Glass shatters/breaks without warning.

I'll have to think about what I want to do there. A rim around the entire top, or maybe an aluminum strap to cross-brace instead. Thanks for that piece to ponder! :thumb:


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## pistolpete (Dec 28, 2009)

i suppose if you were to get a couple of pieces of that security glass with the little wires in it. One to fit inside the glass and one over top. That should be pretty hard to break.

The way I am picturing an aluminum strap ( a solid 1/2 inch by 2 inch piece with 1/4 inch deep slots cut into it and projecting about 1/4 inch past the glass) I think it would look pretty slick and not detract from your clean and crisp vision.


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## BillD (May 17, 2005)

the biggest tank I have seen assembled was a 4' x 8' x 3' high, was made of 1" glass. The base was metal tubing covered with 3/4"plywood, and a layer of styro on that. The bottom of the tank was set right on top of that. The tank was built in place. At some point something must have happened with the bottom piece because it has been patched with a piece placed on top, inside the tank. There is a large hole in the centre of the base for the overflow to come through (about 8 or 12 inch PVC) which is connected to a swimming pool sand filter.
I can't remember how it was braced other than across the width in one or two places. 
As far as glass goes, if you are flexible as to size you may be able to pick up salvage glass for a reasonable price. If you could cheaply get 3 pieces of glass that was 95" x 25" would would you go for it rather than pay full price for the originally planned tank? Cost is always an important consideration for me, so I always look at alternatives. I have 4 tanks that are 48" x 12" x12" (30 gals) because I was able to get 15 pieces of 48" x 12" glass, so I only had to cut end pieces.
For this large tank, it can be eurobraced lengthwise, as well as cross braced which gives more contact area for the cross braces.


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## Gervahlt (Jun 25, 2009)

Thanks for the responses. Yep, cost reduction is definitely part of this project, so finding glass that was close would be fine to me if it costs less. I might even try to find clear coffee table glass to do it, although they're usually not 8' long. Tempered would actually be a good thing in my mind for this project as I have kids and pets. If it broke, I'd rather have dead fish and a room full of water than lacerated dogs and/or kids. If I'm buying it full-price though, I'll go with the traditional plate glass for the sides and tempered for the bottom.

I found some nice aluminum plywood trim today that might work to trim the top of the tank, but I still need to figure out a top support once I get to that point in this project. Maybe I can silicone an aluminum strap across the top and wrap it about 1/4" over the edge, then cover with the trim and silicone it as well.


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