# egg crate or plexiglass at bottom of tank



## ccla (Feb 2, 2009)

As I am getting closer and closer to finally starting to setup the tank, I am reconsidering the use of egg crate at the bottom of the tank.
I have two main reasons for this:

(1) I feel that it would be very hard to clean and or areate the argonite sand that will fall in the eggcrate.

(2) Since I will be installing an Aqua Terra background, I would have to first install the background and then the egg crate. I fear that I will scratch the background while sliding the egg crate in. (I admit this is a rather lame excuse).

So I remember that a while back I read somewhere about using a plexiglass sheet to protect the bottom. I could silicone it in place and then seal the sides with more silicone so that no water would go under it.

Do you guys think this is feasible? Or will I run the risk that the silicone will not create a strong enough bond and will eventually let go of the sheet?
[/list]


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## Morpheus (Nov 12, 2008)

Silicone and plexiglass do not make a happy couple. Silicone does not adhere to acrylic very well. I think eventually the seal would fail.


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## con-man-dan (Aug 19, 2006)

egg crate is easy enough to take a row or two off to accomodate the backround that its a moot issue. If you vacuum carefully, you can "toss" the sand with no problem to prevent pockets of gas/dead matter building up. Plus, most of the waste sits on TOP of the sand. I use egg crate in all my tanks now, good idea especially if you'r eputting large amounts or just heavy rocks in


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## acrosstic (Mar 24, 2008)

There is a little debate about the use of eggcrate.

My opinion, it can't hurt really.

However, I think I is probably more usefull for plate glass bottoms. Tempered glass is crazy strong and even a falling rock likely wouldn't bust it. However, a little pressure the wrong way on plate glass an you have a crack. So the eggcrate does well to avoid this issue.

I plan to silicone mine down, so sand doesn't get underneath it if I use it at all.

I will say I am also debating the use in my new 120, because are we to assume a bed of sand won't spread out the force of a falling rock? Also I have major diggers and eggcrate isn't eye pleasing. It also will cost me $20 in the material. I'm on a tight budget and the last thing I want to do is waste money on something I'll remove from the tank.


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## ccla (Feb 2, 2009)

Morpheus said:


> Silicone and plexiglass do not make a happy couple. Silicone does not adhere to acrylic very well. I think eventually the seal would fail.


So I just cam back from Lowe's and I was looking around in the plexiglass section and what do they sell to glue/seal the plexiglass panels? GE 100% silicone! :-?

Why would they specifically sell that if it does not create a strong bond?

I am going to do a little experiment. I bought a couple of small pieces of plexiglass and I am going to glue them together and see what kind of bond I get.


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## sleepy09 (Jan 15, 2009)

Hi ccla, My vote is to use eggcrate. If you take your time and be careful the add insurance is worth it.

I am using eggcrate in the bottom my tank under the sand. You are right, you will have to be very careful when putting it into your tank. I had to learn that lesson myself. I have a simple plan for the next time that I have to use it in another tank to keep from scratching the glass. I plan on cutting it into smaller pieces and then using a dremmel tool to grind down the edges to make them smoother so that they won't be able to scratch the glass.



> I will say I am also debating the use in my new 120, because are we to assume a bed of sand won't spread out the force of a falling rock?


If you put the eggcrate down and add just enough sand to cover it then put the rock on top of the eggcrate itself you can then put the rest of the sand around the rock. This will help keep your sand diggers from digging under the rock and making them fall. My fish dig around in the sand in my tank all of the time but they never dig under the rocks.

I have about 2-3 inches of sand in my tank and I never see the eggcrate. You don't have to cut it to fit perfectly. Cut it so that there is about 2-3 inches from the outside edge of the tank. That way you won't see it if the fish dig around on the outside edge of the tank.


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## prov356 (Sep 20, 2006)

> I am reconsidering the use of egg crate at the bottom of the tank.


Egg crate is very brittle and won't do anything to strengthen tempered glass. Simplify your 
installation and leave it out. Your tank will hold more rocks than you could ever put into it.

That's my vote


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## Romble (Apr 11, 2007)

I dont know about Eggcrate at the bottom of the tank but I use it for the top of my tanks :wink:

....cut it to fit your filter needs and i use a 48" double flurescent shop lite on top. You can feed the fish right through the top of it or cut a hole big enough to fit your hose for water changes etc.. it is awesome and cheap..

if you want to cover it cause of splashes or evaporation buy styrene/acrylic from the same spot you get eggcrate and glue them or twist tie them together,,,


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## acrosstic (Mar 24, 2008)

tempered glass and sand... No eggcrate... I'm not too worried.


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## ccla (Feb 2, 2009)

ccla said:


> Morpheus said:
> 
> 
> > Silicone and plexiglass do not make a happy couple. Silicone does not adhere to acrylic very well. I think eventually the seal would fail.
> ...


Well I can tell you one thing: I will not silicone a plexiglass sheet at the bottom of my tank. Silicone does not stick for )(*&#* to plexiglass.


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## ccla (Feb 2, 2009)

So I am in the process of cleaning the silicone off of the two plexiglass sheets I used for the test and I notice that in some spots the silicone is really hard to remove.
I take a closer look and I notice that the surface of the plexiglass is not totally smooth, it looks like a pencil eraser scuff where the silicone will not come off.
I figure if this makes the silicone hard to remove (in the other sport it just peels off) then if I scuff the entire surface then the silicone will adhere to the whole surface.
I proceed to use 600 grit paper to go over one side on each sheet and then I silcone them together. Here is the result:










The bond between the two sheets is very strong. There is no way I can tear them apart, no matter how hard I pull.
What I will do in the tank is I will sand one side of the plexiglass and then the edges of the sheet. First I will silicone the sheet down and when it cures, I will seal the edges of the sheet with more silicone. This should work and I believe will provide better shock protection than egg crate.


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## fishEH (Sep 15, 2008)

Why are you bothering to silicone the plexi down at all? Isn't the weight of the sand, rock, and water enough to keep it in place?


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## prov356 (Sep 20, 2006)

fishEH said:


> Why are you bothering to silicone the plexi down at all? Isn't the weight of the sand, rock, and water enough to keep it in place?


He's trying to seal it so he doesn't get nasty anaerobic areas underneath. But, what if it doesn't seal in 
one little spot, and six months or two years in you notice a nasty pocket forming? That'd be a nightmare 
tear down and repair job.


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## ccla (Feb 2, 2009)

You may be right Tim. I probably will skip the plexiglass on the 75g. I may try it on my 10g hospital tank to see if it holds.


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## hankm (Dec 10, 2008)

Has anyone ever heard of a horror story where the bottom of a tank with tempered glass broke because of too many rocks in the tank? Or is the suggestion to place egg crate at the bottom bred mostly out of paranoia?


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## prov356 (Sep 20, 2006)

> Has anyone ever heard of a horror story where the bottom of a tank with tempered glass broke because of too many rocks in the tank? Or is the suggestion to place egg crate at the bottom bred mostly out of paranoia?


You might find a story out there somewhere, but it's incredibly uncommon. And it's not because we're 
all using eggcrate, since many don't.

Check out this thread.


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## hankm (Dec 10, 2008)

Thanks Tim for pointing me towards that thread. I think I'll just forget anyone ever said anything at all about egg crate and forge on ahead. Ignorance is bliss. 
And judging from all the posts on that thread...it sounds like everyone's dealing with hypothetical problems that haven't really presented themselves yet.
Appreciate your help.


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## kimismenos (Jun 25, 2002)

Why so much fuss & debate over this decision? 
Eggcrate is cheap. Just use it, place your rocks on top, then layout your substrate. rest assured your fish can dig all they want and the rocks will not move because they cannot dig under them! now it wont matter if you have low rocks, but for anyone with high stacked rocks, its a must for peace of mind! A must because its cheap insurance, if you don't get it purpose by now, don't bother using it and move on.


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## prov356 (Sep 20, 2006)

> Why so much fuss & debate over this decision?


Looks ugly if exposed, and can trap organics in pockets. And only gives peace of mind if you don't trust 
in the integrity of the tempered glass and believe a piece of plastic will strengthen it.



> if you don't get it purpose by now, don't bother using it and move on


It's not a matter of not getting it's purpose. it's a matter of believing it serves no purpose. Sounds like 
you're tired of hearing from folks that don't believe the same things about eggcrate as you do and you'd 
like us all to just be quiet about it. Since it's an open forum, topics like this will get kicked around over 
and over, and you're likely to hear viewpoints different from your own. Hopefully the day won't come 
when people are intimidated out of contributing a viewpoint that may differ from someone else's. I hope 
everyone continues to express whatever viewpoint they have because that's what makes this a great 
forum. :thumb:


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## kimismenos (Jun 25, 2002)

prov356 said:


> > a piece of plastic


Just about everything that needed to be said, YES its just a piece of plastic, that why you simply USE it or not. when exposed it is far more camouflaged than bare glass so "unsightly" is a non issue. IMO.


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## overleaf (Jan 18, 2009)

I think there is much confusion on the use of eggcrate and not one person here has touched on the true issue.

If you've ever worked in any form of emergency response you know that you carry a steel punch, generally on your keyring. The purpose of the punch is the exert a large amount of energy in a very concentrated area to shatter glass. Believe me, tempered glass is no match for concentrated kinetic energy.

The purpose of the eggcrate is not to 'reinforce' the tempered glass as it obviously cannot do that. The purpose is the prevent concentrated kinetic energy from making contact with the glass. As far as strength, you want to use the acrylic eggcrate because the styrene will crack easier.

For all of those who tell you it spreads the weight across the glass, or that it makes the glass stronger... they're wrong and spewing rubbish. All it does is eliminate the possibility of concentrated energy shattering the bottom of your tank. Nothing more, nothing less.

Also, the risk of the glass shattering without impact is almost 0. The glass is rediculousy strong when the edges are supported properly.

Hope this helps clear this up...


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## prov356 (Sep 20, 2006)

> If you've ever worked in any form of emergency response you know that you carry a steel punch, generally on your keyring. The purpose of the punch is the exert a large amount of energy in a very concentrated area to shatter glass. Believe me, tempered glass is no match for concentrated kinetic energy.


Grains of sand between rocks and tank bottoms aren't blowing out tank bottoms. And to claim that 
eggcrate prevents that, you'd have to show how sand never gets between the eggcrate and the tank 
bottom. These tanks are field tested and proven to be able to hold lots of rocks without eggcrate. And
a manufacturer in that link I posted confirms that. From that thread:



[b:je1dlshc said:


> Narwhal72[/b]":je1dlshc]The bottom glass used is rated for 8000 and 10,000 psi. This is measured off a 1 square inch area. Which means that you would need to have the weight on the pressure point greater than 8000 lbs to break it.


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## nick a (Apr 9, 2004)

Still trying to spread logic and reason, Tim? You've got the patience of a saint!

I've given up on this and most other debates in favor of just enjoying my fishroom full of fish in tanks sans eggcrate :lol:

Just as an aside; after all these tanks & years, the only tank that's ever failed on me was a 10 gal fry tank. Nothing in it but some plastic plants & a sponge filter. It was a side panel that cracked--not the bottom. Wrote it off as defective glass and spent the $10 for a new one :thumb:


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## overleaf (Jan 18, 2009)

prov356 said:


> > If you've ever worked in any form of emergency response you know that you carry a steel punch, generally on your keyring. The purpose of the punch is the exert a large amount of energy in a very concentrated area to shatter glass. Believe me, tempered glass is no match for concentrated kinetic energy.
> 
> 
> Grains of sand between rocks and tank bottoms aren't blowing out tank bottoms. And to claim that
> ...


The grains of sand aren't solid enough to transfer the impact. They are also static. Kinetics are required.



prov356 said:


> [b:12swnilk said:
> 
> 
> > Narwhal72[/b]":12swnilk]The bottom glass used is rated for 8000 and 10,000 psi. This is measured off a 1 square inch area. Which means that you would need to have the weight on the pressure point greater than 8000 lbs to break it.


[/quote]

Again, those are static loads they're testing.

Here are some structural papers for you:

http://books.google.ca/books?id=xHfU2LT ... 0#PPA95,M1

That shows that it take 1-10JÂ² to break glass. It's probably greater with tempered glass.

How to calculate kinetic energy: http://www.newton.dep.anl.gov/askasci/p ... y99032.htm

I used a 15lb rock in my example for a total of 151.5 joules, calculated at approximately 1s velocity under gravity. Concentrate that on a small area... kaboom. You could drop a 90 pound flat object on flat glass and not have it break providing it was supported properly. The problem arises when it's a pointed area, like the edge of a rock (why punches are so effective). A good example is: a child wearing running shoes can stand on your back, it doesn't hurt at all. Now replace the shoe with a stiletto... ow.

At the end of the day the likelihood of a falling rock causing a structural failure is very low. I don't want to find out what it's like to have > 140G of water in my living room.


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## prov356 (Sep 20, 2006)

[b:2bxh0e4m said:


> nick a[/b]":2bxh0e4m]Still trying to spread logic and reason, Tim? You've got the patience of a saint!


Yeah, I swore off eggcrate posts a while back, but guess I fell off the wagon.  I think the reason that 
I can't get off of the eggcrate issue is that I continually see posts that direct newcomers to the hobby 
to use eggcrate. I'm giving them another side to the debate, so we don't all appear to be in favor. It's 
more for the lurkers. I'll never convert the eggcrate users. 



[b:2bxh0e4m said:


> overleaf[/b]":2bxh0e4m]You could drop a 90 pound flat object on flat glass and not have it break providing it was supported properly. The problem arises when it's a pointed area, like the edge of a rock


Sounds like the risk now is to breakage from a falling rock. I thought the risk was from grains of sand.

Everyone needs to decide for themselves and I don't care what they decide, but I just dispute the 
claim that a rock sitting on a grain of sand can blow out a tank bottom. I also tend to believe the ones 
making the tanks that a falling rock, at worse, may chip the glass. If you read the entire thread I 
linked, he makes some good points about how glass tanks are well field tested, and if there was a 
need to improve the design and it could be done economically, they would have done so. It's going 
to take more than kinetics formulas and papers to convince me or the ones making the tanks 
otherwise. There's no need to spend money solving a problem that doesn't exist.



[b:2bxh0e4m said:


> overleaf[/b]":2bxh0e4m] I don't want to find out what it's like to have > 140G of water in my living room.


Nobody does, but you're using scare tactics to garner support for your argument. Comes back to the 
'peace of mind' argument. Some have it with eggcrate and some have it without. Bottom line, neither 
one's tanks are blowing out from falling rocks, or grains of sand, or we certainly would be hearing 
about it here. Tank blowouts are incredibly rare, and the only ones I've read about were caused by 
issues other than rocks or sand.

I've presented my side, so I'll back off and let the reader's decide. I hate eggcrate threads.


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## zinn250 (Feb 16, 2009)

I wasn't going to post to this, because I agree that it really is a personal choice. In this case though, I have to agree with both Overleaf and Prov.

No, eggrate will in no way strengthen your tempered glass. Prov is right - you will never be able to "overload" your tank with rocks to the point that it will blow out your tempered bottom. Nor will a grain of sand trapped between the eggcrate and your tank bottom cause catastrophic failure.

That said...a rock with a sharp point falling and hitting your tempered bottom could cause it to explode. Tempered glass is stronger in the center than it is on the edges, and depending on the size of your tank, the bottom pane of glass can hold up to 345 lbs per square foot! So - you don't need to worry about too much weight, you just need to be concerned with falling rock. I think that's why so many people favor the use of eggcrate in tanks where you have stacked rock formations. Better safe than sorry, in my opinion 

To each his own though!! :thumb:


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## prov356 (Sep 20, 2006)

> That said...a rock with a sharp point falling and hitting your tempered bottom could cause it to explode. T


Although it sounds logical, the force needed would be incredibly difficult to come by from a falling rock in 
an aquarium. Maybe in theory, but practically impossible. Water and sand would soften the blow. 
Rocks typically tumble, then don't fall from heights. In theory, it's possible to take a large rock and hold it 
up a certain height with the pointed side down and break the glass, I suppose, but you'd almost have to 
go out of your way to do that. Empty the tank of water, remove all sand, etc, and hold a rock above it, and 
let it accidentally slip out of your hand, then ok, I'll agree.


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## ccla (Feb 2, 2009)

prov356 said:


> > That said...a rock with a sharp point falling and hitting your tempered bottom could cause it to explode. T
> 
> 
> Although it sounds logical, the force needed would be incredibly difficult to come by from a falling rock in
> ...


Tim,

that is the conclusion I came to as well. No crate or plexiglass for me. Unfortunately I have already bought and cut the eggcrate down to size so I have wasted $10. Luckily I have not bought the plexiglass; that would have been over $40 out the window.


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## Hoggy Boss (Oct 4, 2006)

Eggcrate can also be used for stability. I think the tank could support the weight without using eggcrate, but I find useful when it comes to setting up the rocks. The empty spaces in the eggcrate do a better job of securing points of the rock that the glass cannot. This allows me to make more hiding areas.


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