Question About Building Glass Aquarium

[fishguy306]

Some of your logic doesn't make sense...

The floating bottom design is actually prone to failure for several reasons.
The most obvious is the weight of all the water in the tank is being held by the silicone on the bottom pane of glass.

How is this different than if the sides are on top of the glass? The water is going to be pushing out against the silicone instead of down. As I said in my post, it is shear vs tensile strength. With a good silicone both will be high enough to not make a difference.

A not so obvious reason for failure is the fact that, in addition to the water weight, decor and substrate, any upward force would have an equal stress factor....like when people put styrofoam under their tanks.

Water pressure is by far the biggest issue here, even on a large tank the couple hundred extra pounds of substrate wont make a difference in the grand scheme of things. Further if you properly set up your tank you wont use foam under a tank with a floating bottom or a rim, it is unneeded and just causes twisting and stress on the tank.

Placing the sides of the tank on top of the bottom piece actually gives you more surface area to apply silicone.

How do you figure? If you are building a tank out of 1/2" glass you are going to have 1/2" seam in either build style. Silicone will only be as wide as the glass is, or at least the silicone that holds the tank together.

Placing the end glass inside the front and rear panels is a matter of opinion and I am of the opinion that strength isn't the reason, moreover, it is the fact that glass is purchased in standard lengths and having to remove an inch from a 36", 48", 60", 72"....etc...is more work. It is also my opinion that the exposed edges of glass is better viewed from the side than the front.

Strength isn't the reason at all as it wont matter. Either way you have a seam. Glass does not come in those standard lengths, it comes in 96x48" sheets and is cut down as needed. Anything other than that is custom. A glass shop cuts the sheets down as needed. Whether you are going 72" or 71" wont make a difference.

Everything that is done to commercial built tanks is done for two reasons mainly:
-Build cost
-Liability
Liability is a risk factor that determines how the manufacturer builds the tank and they go by industry standard and experienced past failures. The point is, if you are building a tank on your own, it would be wise to "copy" the building standards of current manufacturers. ..they have paid their dues most likely and so-to-speak.

Many aquarium builders, especially the common and not custom made tanks are built with a floating bottom. Vast majority in fact. Why do you think you aren't supposed to put foam under a rimmed with plastic tank? If you were to remove the bottom trim most of the time you will find the bottom is inside the sides of the tank.

 

[boldtogether]

Some of your logic doesn't make sense...



How is this different than if the sides are on top of the glass? The water is going to be pushing out against the silicone instead of down. As I said in my post, it is shear vs tensile strength. With a good silicone both will be high enough to not make a difference.



Water pressure is by far the biggest issue here, even on a large tank the couple hundred extra pounds of substrate wont make a difference in the grand scheme of things. Further if you properly set up your tank you wont use foam under a tank with a floating bottom or a rim, it is unneeded and just causes twisting and stress on the tank.



How do you figure? If you are building a tank out of 1/2" glass you are going to have 1/2" seam in either build style. Silicone will only be as wide as the glass is, or at least the silicone that holds the tank together.



Strength isn't the reason at all as it wont matter. Either way you have a seam. Glass does not come in those standard lengths, it comes in 96x48" sheets and is cut down as needed. Anything other than that is custom. A glass shop cuts the sheets down as needed. Whether you are going 72" or 71" wont make a difference.



Many aquarium builders, especially the common and not custom made tanks are built with a floating bottom. Vast majority in fact. Why do you think you aren't supposed to put foam under a rimmed with plastic tank? If you were to remove the bottom trim most of the time you will find the bottom is inside the sides of the tank.

I don't think foam is a good idea and the vast majority of tanks I have purchased place the glass under the sides. Placing the glass under the sides allows tensile strength to keep the sides, front and back from separating...
Standard glass is cut up as efficiently as possible without waste. Manufacturers standardize cuts for whatever tank size is going to be built. If you order a standard tank based on gallons most likely you will get one built on an assembly line, from glass cut for multiple tanks. Cutting glass at custom lengths adds cost if more than one standard sheet is needed....and depending on top and bottom framing, which is also standardized, the tanks can only be built one way.
The only tanks I have ever had fail at the bottom, where floating bottom and I haven't seen one built like that in a long time. Even acrylic tanks are built, in my experience, with the bottom non-floating.

 

[fishguy306]

Placing the glass on top of the bottom would actually be dealing with shear strength, not tensile. And regardless, that strength is still present with the glass built around the bottom, just with tensile instead. I can look up the MSDS for RTV 108 if you need the proof on this.

These days you are right, foam under most tanks is a bad idea. Rimmed tanks should not have any foam under them for any reason. Vast majority of rimmed tanks also have a floating bottom, you just can't see it due to plastic trim.

And you are correct with big tank builders, they do try to make the most out of every piece of glass. That said the is about building a custom tank. You wouldn't go to aqueon or oceanic for your glass pieces or to have a tank made. You'd go to a glass shop. Nearly every glass shop will charge you the exact same for a 71" piece as a 72".

Acrylic is a totally different animal than glass and is not really comparable in this case. But you are correct, acrylic is built on the bottom.

 

[Lepisosteus]

acrylic is not part of this, glass aquariums is the topic

 

[Lepisosteus]

I don't think foam is a good idea and the vast majority of tanks I have purchased place the glass under the sides. Placing the glass under the sides allows tensile strength to keep the sides, front and back from separating...
Standard glass is cut up as efficiently as possible without waste. Manufacturers standardize cuts for whatever tank size is going to be built. If you order a standard tank based on gallons most likely you will get one built on an assembly line, from glass cut for multiple tanks. Cutting glass at custom lengths adds cost if more than one standard sheet is needed....and depending on top and bottom framing, which is also standardized, the tanks can only be built one way.
The only tanks I have ever had fail at the bottom, where floating bottom and I haven't seen one built like that in a long time. Even acrylic tanks are built, in my experience, with the bottom non-floating.

a few things. A floating bottom aquarium does not have the sides and front panels lower then the bottom. they are all flush with the bottom so the weight of the water and the tank only being on the sides of the tank is incorrect. The force will still be exerted over the entire area of the aquarium. In my opinion both ways will result in the same amount of force on the glass. They both have the same amount of silicone, and unless mathematically corrected I feel there is no difference. The only thing I could think of is as the water pushes out on the glass panels being outside of the bottom, is that the bottom 1/2" of glass or so may act in providing leverage on the silicone where they meet.

 

[boldtogether]

First of all...tensile strength is how much silicone will stretch, therfore, the silicone used in the corners and "tooled" with the finger or actual tool is what would stretch when pressure is exerted from the inside.
Shear strength is the ability to resist a "sliding failure along a plane that is parallel to the direction of the force"...in an aquarium application, shear strength is what is relied on to keep the bottom edges of glass (in a solid construction) from sliding out under pressure. If the glass is placed on the outside edges of the bottom pane of glass, the shear strength properties of the silicone is not being utilized. The silicone between the panes will stretch as will the silicone in the corners. Shear will only be a factor on the end panes if, and o ly if, the panes are on the inside of the front and rear panes...in a floating bottom construction.
The idea of a solid bottom construction is to utilize both tensile and shear strength of the silicone. The advantage of solid bottom construction also is the addition of silicone on the outside of the joint, when a frame is used. The frame on large aquariums is not only for aesthetics, but also to prevent chipping. Most frames on most large tanks are individual mitered pieces. Attached to the outside edges of the joints gives added silicone sealant to the joint both top and bottom.
So is solid better than floating? The high end tank makers believe so and reflect that in their construction, otherwise it wouldn't be considered a selling point. Mass produced imported tanks from Asia and Europe are built floating for many reasons, but US made tanks like Visio deliberately build their tanks with solid bottom construction.
All engineering considerations aside, building a tank from scratch as a DIY project is more about execution than anything to be successful.

 

[boldtogether]

acrylic is not part of this, glass aquariums is the topic

I wasn't compairing I was making an observation and you may disagree, but the construction considerations are very much related for the same reasons.

 

[Tech]

When I built all the glass aquariums I have I always put the glass sides and fronts on top of the bottom panel. Does anyone put them beside the glass panel? What are the pros and cons?

I have, I built my first few with a raised bottom like normal aquariums but that was only because I was copying their design. I don't see any benefits to it unless you are using a bottom trim piece.

The reason they build them that way is because the edges of glass are much more vulnerable to damage than the flat sides. By trimming the edges in plastic they protect them and likely prevent many failures. Protecting the edges from damage is a key consideration when building your own tanks, even with thick glass a relatively minor impact on an edge can crack a pane.

A not so obvious reason for failure is the fact that, in addition to the water weight, decor and substrate, any upward force would have an equal stress factor....like when people put styrofoam under their tanks.

I think you're mistaken here. Placing Styrofoam under the tank is going to alleviate most all of the weight on the bottom seam by transferring the water/substrate weight directly from the tank, though the glass, into the foam, and into the stand. The only force left the silicone on the bottom pane must support is the weight of the sides of the tank which is comparatively no weight at all.

 

[xraycer]

I have no experience or scientific facts to say which method is better, but from purely a mechanical perspective, I would think that the advantage to having the 'side panes on top of the bottom' should result in less stress to the seams when the tank is lifted and being moved around

 

[boldtogether]

I have, I built my first few with a raised bottom like normal aquariums but that was only because I was copying their design. I don't see any benefits to it unless you are using a bottom trim piece.

The reason they build them that way is because the edges of glass are much more vulnerable to damage than the flat sides. By trimming the edges in plastic they protect them and likely prevent many failures. Protecting the edges from damage is a key consideration when building your own tanks, even with thick glass a relatively minor impact on an edge can crack a pane.




I think you're mistaken here. Placing Styrofoam under the tank is going to alleviate most all of the weight on the bottom seam by transferring the water/substrate weight directly from the tank, though the glass, into the foam, and into the stand. The only force left the silicone on the bottom pane must support is the weight of the sides of the tank which is comparatively no weight at all.

I am not mistaken. This debate has been going on for many years in many forums. It doesn't matter if I used to work for an aquarium builder as a line assembler. It doesn't matter if I regularly visit my very good friend Russ at his glass shop and talk about this very thing and why he has stopped the floating design when he is commissioned to build an aquarium. It doesn't matter that the only failures I have had with tanks I have bought were floating bottom design, with and without foam. All the aquariums I have built, including my 500g acrylic (yeah, I said acrylic) have been a success, except the 125 I built as a floating bottom.
I'm not talking from my ass about this subject and I'm not just msking it up as I go along. I have been in this hobby for 40 years and 10 of those were a business.
This debate is going to end for some people when their floating design fails and some people will never experience a fail in their entire fish keeping life. Others will experience constant fails with glass tanks and switch to acrylic and swear by that construction. And then there will be those of us, myself included, that have experienced fails in both designs and both materials but continue to persue the hobby because that is just part of the hobby.
I would suggest, and just my opinion, construction of your own aquarium be done in a clean, well lit dedicated area and have a concise, well thought out plan before during and after construction.
But, be prepared for catastrophic failure at least as something that could happen and sometimes does even to the best construction.
This debate, like the add-salt-to-freshwater debate, the should-I-use-a-bubbler debate, is-bare-bottom-better-than-substrate debate are never ever going to be resolved or "won" because there are too many people with too many experiences, too many variables and too many opinions.
Do the best you can and make the best determination based on your gut feeling and just go with that prepared to accept whatever happens after......or doesn't happen.
...out