Aquarium Decoration (Rocks, Plants and Substrates) • Two Questions About Rocks

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Two Questions About Rocks

Postby Smeagol » Sat Feb 06, 2021 6:07 pm

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.
ROCK02.jpg
75g = Yellow-tail Acei, Yellow Labs, Maingano
20g Planted = Harlequin Rasboras, Lemon Tetras, Amano Shrimp
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Re: Two Questions About Rocks

Postby Stu W2 » Sat Feb 06, 2021 6:34 pm

Some sort of shale perhaps?

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Re: Two Questions About Rocks

Postby DJRansome » Sat Feb 06, 2021 7:15 pm

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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Re: Two Questions About Rocks

Postby Smeagol » Sat Feb 06, 2021 9:17 pm

DJRansome wrote: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 wrote:Some sort of shale perhaps?

You're on the right track. I think it's "red mudstone," which is closely related to shale.
75g = Yellow-tail Acei, Yellow Labs, Maingano
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Re: Two Questions About Rocks

Postby Auballagh » Sat Feb 06, 2021 9:35 pm

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
Image
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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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Re: Two Questions About Rocks

Postby Auballagh » Sat Feb 06, 2021 9:42 pm

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...

:o ROCKFALLS!!!! :o
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Re: Two Questions About Rocks

Postby Smeagol » Sat Feb 06, 2021 10:19 pm

Auballagh wrote: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 wrote: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. :D
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Re: Two Questions About Rocks

Postby Idech » Sat Feb 06, 2021 10:59 pm

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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Re: Two Questions About Rocks

Postby DJRansome » Sat Feb 06, 2021 11:18 pm

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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Re: Two Questions About Rocks

Postby Smeagol » Sat Feb 06, 2021 11:28 pm

Idech wrote: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.
75g = Yellow-tail Acei, Yellow Labs, Maingano
20g Planted = Harlequin Rasboras, Lemon Tetras, Amano Shrimp
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Re: Two Questions About Rocks

Postby Stu W2 » Sun Feb 07, 2021 2:32 am

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.

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Re: Two Questions About Rocks

Postby Idech » Sun Feb 07, 2021 10:01 am

Stu W2 wrote: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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Re: Two Questions About Rocks

Postby Smeagol » Sun Feb 07, 2021 10:25 am

Idech wrote:
Stu W2 wrote: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.


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.
75g = Yellow-tail Acei, Yellow Labs, Maingano
20g Planted = Harlequin Rasboras, Lemon Tetras, Amano Shrimp
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Re: Two Questions About Rocks

Postby Auballagh » Sun Feb 07, 2021 12:15 pm

Oh man, really....? It's the egg crate thing again?!!! :oops:
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. :oops:
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Re: Two Questions About Rocks

Postby Idech » Sun Feb 07, 2021 2:21 pm

Smeagol wrote: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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