# Two Questions About Rocks



## Smeagol (Jan 23, 2021)

1) Does anyone know what kind of rock this is? I bought a few hundred pounds of it at a local "mom & pop" garden center. (I bought way more than I need, but I wanted to have lots of various shapes and sizes available for stacking.) It's all reddish-brown, with some very noticeable stratification lines. I asked the proprietor what kind of rock it is, but he didn't know. All he could tell me is that it comes from Pennsylvania, and that it's pure natural rock (no dyes or cleaners or anything).

2) Who knew rocks are so heavy?! :wink: I'm terrified to put them in my tank! How much weight can the bottom glass of a standard 75-gallon tank support without cracking?

I don't know why the picture is upside-down. If you click on it to enlarge it, it will be right-side-up.


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## Stu W2 (Nov 17, 2020)

Some sort of shale perhaps?

Regards,
Stu


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## DJRansome (Oct 29, 2005)

Water weighs a lot too, the rocks don't weigh all that much more. You could fill the tank with rocks and stand on top and the glass would not break. Floors are usually fine, but that could be something to check more than the tank.


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## Smeagol (Jan 23, 2021)

DJRansome said:


> Water weighs a lot too, the rocks don't weigh all that much more. You could fill the tank with rocks and stand on top and the glass would not break. Floors are usually fine, but that could be something to check more than the tank.


Yeah, but the water weight is evenly distributed. A big rock (or pile of rocks) might create a stress point, no?



Stu W2 said:


> Some sort of shale perhaps?


You're on the right track. I think it's "red mudstone," which is closely related to shale.


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## Auballagh (Jan 29, 2003)

It could be mudstone. I'm more inclined to believe its a closely related sedimentary rock called 'Siltstone'.
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Siltstone








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Mudstone








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Mudstone looks more like shale. And, is normally found along with shale deposits. Siltstone is typically located near sandstone areas. Mudstone, Shale and Siltstone are all completely safe rock for aquarium use. Chemically Inert, they will not influence PH or react with water.


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## Auballagh (Jan 29, 2003)

Oh, and as for building the rock pile in your tank? Yes, those rocks are indeed, freaking heavy! Build and set up your rock piles and formations - BEFORE - you place any sand or gravel in the aquarium. The rocks are just (gently) placed right on top of the glass. Once you are set and happy with the rocks, then add substrate to the desired depth. Doing that will keep determined Cichlid diggers from undermining your rockpiles, which can potentially cause catastrophic...

 _ROCKFALLS!!!!_


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## Smeagol (Jan 23, 2021)

Auballagh said:


> It could be mudstone. I'm more inclined to believe its a closely related sedimentary rock called 'Siltstone'.


According to the articles I read, siltstone isn't fissile like mudstone. This rock (that I bought) _is _fissile; the stratification lines are striking.



Auballagh said:


> Mudstone, Shale and Siltstone are all completely safe rock for aquarium use. Chemically Inert, they will not influence PH or react with water.


Thanks! That was my next question.


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## Idech (Nov 8, 2020)

I like to put the rocks on egg crate, not directly on the glass. You can buy it at Home depot or they have it pre-cut on Amazon. I needed 5 packs of 4 for my 75 gallons if I remember correctly. You put the egg crate first (I don't know why they call it egg crate, it's the plastic crates that covers light bulbs in commercial settings), then you put the rocks on it and the sand is last. This way nothing is ever going to fall and the glass won't be damaged.


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## DJRansome (Oct 29, 2005)

I used to use egg crate as well, but the engineers on this forum convinced me that it does not have a benefit and it looks ugly when the fish dig it up.

You are going to fill the tank with rocks so there will not be a single pile balanced on a point to create a problem.


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## Smeagol (Jan 23, 2021)

Idech said:


> I like to put the rocks on egg crate, not directly on the glass. You can buy it at Home depot or they have it pre-cut on Amazon. I needed 5 packs of 4 for my 75 gallons if I remember correctly. You put the egg crate first (I don't know why they call it egg crate, it's the plastic crates that covers light bulbs in commercial settings), then you put the rocks on it and the sand is last. This way nothing is ever going to fall and the glass won't be damaged.


I've read a few debates about the use of egg-crate, and I decided not to use it. First, I'm not too concerned about falling rocks. I have such a variety of shapes & sizes that I'm confident I'll be able to stack them in a stable arrangement. I'm only concerned about the concentration of weight, and I'm not convinced that egg-crate solves that problem (if it even is a problem). And how do you clean the sand in the egg-crate? And what about when fish dig and the egg-crate becomes visible? Seems like there are more cons than pros.


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## Stu W2 (Nov 17, 2020)

My experience with the white plastic version of egg crate, in marine and freshwater aquarium, both with fine crushed coral substrate, was very satisfactory. The rare time that some of it showed it was easily covered over again with the use of a long handled plastic kids beach shovel that I kept handy for just such tasks.

Regards,
Stu


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## Idech (Nov 8, 2020)

Stu W2 said:


> My experience with the white plastic version of egg crate, in marine and freshwater aquarium, both with fine crushed coral substrate, was very satisfactory. The rare time that some of it showed it was easily covered over again with the use of a long handled plastic kids beach shovel that I kept handy for just such tasks.
> 
> Regards,
> Stu


That's what I figure. I have almost 3 inches of sand and the egg crates are below the black band on the tank so I don't see how they could be visible in any ways, even if the fish dig very deep.

But, to each their own as they say. As long as you're happy with your setup.


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## Smeagol (Jan 23, 2021)

Idech said:


> Stu W2 said:
> 
> 
> > My experience with the white plastic version of egg crate, in marine and freshwater aquarium, both with fine crushed coral substrate, was very satisfactory. The rare time that some of it showed it was easily covered over again with the use of a long handled plastic kids beach shovel that I kept handy for just such tasks.
> ...


My understanding is that you shouldn't have 3 inches of sand. In planted tanks, you need a deep substrate for plants to root. But from what I've read, the conventional wisdom is you should only have 1 to 1.5 inches (max) of sand for mbuna cichlids. But I'm just a newb here; please correct me if I'm wrong.


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## Auballagh (Jan 29, 2003)

Oh man, really....? It's the egg crate thing again?!!!  
C'mon... I thought that glass busting myth about heavy rocks chiseling down through and shattering the bottoms out of aquariums had been well, Busted? :roll: 
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I mean through the late 90' and into the mid-2000's egg crate was definitely the thing. We all thought that surely only a FOOL would risk placing those heavy rocks against glass like that, right? I even personally took it a step further, and actively disparaged the use of bottom egg crate by installing a siliconed-in sheet of plexiglass over the bottom glass of my Mbuna tanks (they were a 110XH, and then I 'graduated' to a 150XH). The bottom plexi sheet was supposed to provide this so-called sacrificial scratching layer for the rocks to dig into - protecting the bottom glass.
Ridiculous! And, it was all a bunch of OVER-KILL. Totally unneeded! Trust me, the tempered glass on the bottom of your aquarium can totally handle the weight. Just be gentle when placing the rocks down.
Now, for the sides of your aquarium? Oh man.... Not So Much!
So, if a heavy rock tumbles down off the rockpile, and crashes into the side of your tank? Whew... then you could be in real trouble. Be careful of that.


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## Idech (Nov 8, 2020)

Smeagol said:


> My understanding is that you shouldn't have 3 inches of sand. In planted tanks, you need a deep substrate for plants to root. But from what I've read, the conventional wisdom is you should only have 1 to 1.5 inches (max) of sand for mbuna cichlids. But I'm just a newb here; please correct me if I'm wrong.


Since cichlids like to dig, 2-3 inches is recommended from what I have read. I don't see how having that much sand would cause any problems. My fish like to make deep pools in the sand to breed, so I'm happy I gave it to them.


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## Idech (Nov 8, 2020)

Auballagh said:


> Oh man, really....? It's the egg crate thing again?!!!
> C'mon... I thought that glass busting myth about heavy rocks chiseling down through and shattering the bottoms out of aquariums had been well, Busted? :roll:
> -
> I mean through the late 90' and into the mid-2000's egg crate was definitely the thing. We all thought that surely only a FOOL would risk placing those heavy rocks against glass like that, right? I even personally took it a step further, and actively disparaged the use of bottom egg crate by installing a siliconed-in sheet of plexiglass over the bottom glass of my Mbuna tanks (they were a 110XH, and then I 'graduated' to a 150XH). The bottom plexi sheet was supposed to provide this so-called sacrificial scratching layer for the rocks to dig into - protecting the bottom glass.
> ...


I like overkill. I don't want the bottom of my tank to be all scratched, even though it's not visible. I didn't do it thinking the glass couldn't handle it as this doesn't make sense; the weight is the same with or without egg crate.


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## Smeagol (Jan 23, 2021)

Idech said:


> Smeagol said:
> 
> 
> > My understanding is that you shouldn't have 3 inches of sand. In planted tanks, you need a deep substrate for plants to root. But from what I've read, the conventional wisdom is you should only have 1 to 1.5 inches (max) of sand for mbuna cichlids. But I'm just a newb here; please correct me if I'm wrong.
> ...


I'm pretty sure I read it in a few threads on this forum.... something about organic waste getting trapped in sand if it's deeper than 1" or so...???


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## Smeagol (Jan 23, 2021)

Auballagh said:


> Oh man, really....? It's the egg crate thing again?!!!
> C'mon... I thought that glass busting myth about heavy rocks chiseling down through and shattering the bottoms out of aquariums had been well, Busted? :roll:
> -
> I mean through the late 90' and into the mid-2000's egg crate was definitely the thing. We all thought that surely only a FOOL would risk placing those heavy rocks against glass like that, right? I even personally took it a step further, and actively disparaged the use of bottom egg crate by installing a siliconed-in sheet of plexiglass over the bottom glass of my Mbuna tanks (they were a 110XH, and then I 'graduated' to a 150XH). The bottom plexi sheet was supposed to provide this so-called sacrificial scratching layer for the rocks to dig into - protecting the bottom glass.
> ...


Man, I hope you're right! Because these rocks seem ridiculously heavy to me.


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## Idech (Nov 8, 2020)

Smeagol said:


> Idech said:
> 
> 
> > Smeagol said:
> ...


Well, I've had deep bed aquariums for decades and it's always worked well for me. Mind you it was planted tanks but it's just as well with rockscape. You just need to be careful not to go too deep when vacuuming. Also, I have two powerheads in the tank to make sure waste gets filtered. And I'm planning on addind a third one. So waste won't be a problem !

Waste would be more of a problem if the substrate was gravel, as it slips into the cracks and won't be moved by water movement into the filter inlet. I wouldn't have a deep bed of gravel. I have aragonite sand (special grade, which is smaller than regular aragonite).


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## DJRansome (Oct 29, 2005)

Note that you have to be careful not to go too deep. This way any toxins are not disturbed. I would think the Malawi will go all the way to the bottom as usual.


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