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Scienceman

Rocks: How many (002)

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I am setting up my first 6'X18'X20' tank and am planning on using quite a lot of rocks. Should I be concerned about putting too many rocks in and risk breaking the glass at the bottom of the tank? The tank will be on a regular timber stand which supports the outside edge and has a cross piece at ~ 3' down the length.

Of interest, I have found at a local landscape supplier, a rough granite in thin plates (1-3cm thick). They sell them covered with moss but many pieced were cleanish and they came up well after boiling and scrubbing. This material will allow me to create a lot of crevices without as much rock bulk. I will post a pic when it has been set-up. laugh.gif

Cheers,

Scienceman

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i think the most important thing is that your stand can support the weight and also it depends a lot on how many fish you have in your tank as you dont want to take up too much space if you have a lot of fish. Also fish become more territorial the more caves and rock formations you have , at least so i have found but again it depends on the species you have

cheers

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in my experience i have found there are many things to consider when using alot of rocks.

cleaning underneath them, whether or not the tank will support the weight,if the fish will cause a well balanced structure to collapse, fish getting stuck and probably more that i have overlooked.

some solutions

use less but larger rocks, silicone them together, use a spare undergravel filter or eggcrate etc. to distribute the weight of the rocks over an larger area instead of the contact points on the glass bottom, every four water changes do a big change where you remove and clean under the rock work.

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Thanks for the suggestion to use a flat support to distribute the weight evenly over the bottom. Maybe a piece of foam like that used under the tank would work?

I was planning on building it up as I added fish but I can see that it is a very dynamic situation with many variables.

I did not think that cleanning under it would be a problem but now I think about it, dismantling it on a regular basis is not something I want to do, especially given the risks. I might try and make the crevices large enough to suction directly when I clean. Or perhaps use something to "blow" water in the crevices to move the waste out where it can be suctioned up.

I have had a dry run, assembling the rocks on a table and find that because they are large and flat they are very stable (as tested by vigerous rocking of the table equivalent to a class 6 earthquake!). Given that they will weigh less in the water I am confident that it will be structurally secure.

Cheers,

Scienceman thumb.gif

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I was under the impression that whether you put rocks in your tank or not wont make a massive difference in tank weight once it is full because however many kilos of rock you put in will be equally matched by the amount of water displaced.

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thats right blakey boy the more rocks you put in the more water youll displace, although the rocks are a little bit heavier than the displaced water, one thing to look out for is dont make a 300lt tank into a 200lt with excess rock, careful placement of 4 or 5 largish rocks will create enough cover for everyone, and put eggcrate under them!

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G'day Scienceman,

When I did my 6x2x2, I put a full sheet of 20mm ply supported by the edge rectangular frame and three cross members, one in the center and then one each side of that spaced equally between the center and ends.

The rocks do displace the equivelent amount of water but depending on what kind of rock determins whether it's going to be heavier or lighter, but in the big picture it won't be a huge difference. The water itself does have a supportive effect on the rock work as well.

The egg crate suggestion by Katanaone is one I used with big rocks and works well.

The amount of rock in the tank will be determined by a combination of what your frame, floor and tank can take balanced by what fish you intend on keeping. Are you keeping big fella's that need lots of swimming space or smaller guys? If you are going to have a variety of sizes then you have to put in at least enough to create sufficient hiddy-holes for the small guys when the big guys get too rough. I'm sure you know what I mean.

cheers

glenn

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Thanks Glenn. I'm a bit ignorant on the egg crates as the only ones I have seen were made of cardboard blink.gif I bet my wife will know!

I intend to keep a mixture of big fellas (Aulonocara + Blue Dolphin) and e.yellows. I was planning to put rocks up one end of the tank with small caves for the e.yellows, a long hollow split log down the center and some a couple of big cave rocks down the other end for the Aulonocara. The center of the tank will be pretty open for swimmers.

How does this sound?

(I am open to suggestions of other fish to stock but they must be med-low aggression)

Cheers,

Scienceman

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using alota of rocks it is unsafe to lean any rock on side walls is this right?

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I don't lean any rocks on the side/back glass EVER, as this will only scratch the glass in time.

When stacking lots of rocks, I like to choose rocks which have fairly flat bottoms and place them on the sand. I then twist/slide the rocks until I have moved most of the sand from under them and the rock is just touching the glass, but this still leaves sand packed under any parts of the rock which is not touching the glass.

Choosing the flattest bottomed rocks for the base of your structure means fish are not as likely to dig under them, which means the structure is less likely to collapse.

I never remove my rocks from the tank, and cleaning under them is a non-event as there is no room for any gunk under them.

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Egg crate is another name for light diffuser's that come in a square grid type pattern, you see them covering fluro's sometimes in office buildings. It's made of hard plastic and comes in sheets. Go to a perspex dealer and see if they have off-cuts. Much cheaper.

glenn

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