What kind of rocks to use? - The Planted Tank Forum
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post #1 of 7 (permalink) Old 10-30-2012, 01:51 AM Thread Starter
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What kind of rocks to use?

I have a 40 breeder with Victorian Cichlids that has black blasting sand for a substrate. I have several anubias in the tank, but the fish keep digging them up. The plants spend more time floating at the top than they do in the substrate. I was wanting to get some rocks and use them in strategic places around the plants so the fish couldn't uproot them, but I don't know what kind to use. I was thinking that a fairly dark gray or black rock would look best, since I think a lighter rock or a brownish rock wouldn't look good with the black sand.

Any suggestions as to a good looking aquarium safe rock would be appreciated. Oh, and I would prefer cheaper rocks, not rocks like Seiryu.
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post #2 of 7 (permalink) Old 10-30-2012, 03:16 PM
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Go to landscape stores, masonry places, rock yards and so on.
Most of the rocks sold there, in bulk or in bags are aquarium safe.

Lake Victoria water is harder and a bit more alkaline than many of the tanks people keep plants in, so even a rock that will add minerals like calcium or magnesium to the water will not be a problem.

If you can get a few broken chunks, samples that you can bring home and test that would be great. Put these samples in separate jars of water and test at the beginning and every few days for pH, GH, KH and TDS. Minor changes in these should not be a problem for hard water fish, but if they change a lot that might be too much.

Anubias should not be planted in the substrate. The roots are better at anchoring to rock or driftwood, not into the substrate so much.

I would get the rock you want, then use the gel type of superglue to attach the Anubias.
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post #3 of 7 (permalink) Old 10-30-2012, 04:12 PM
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For a Victorian tank, rocks that raise KH/GH/TDS are not going to be an issue. You could put straight limestone in there with crushed coral and the buffering effect from those would be beneficial.

I would recommend something that is sold by the trade name "Texas holey rock" which is a limestone that has nice holes in it. It should be readily available at most landscape rock places. Depending how dirty it is, it will probably not look very attractive when you buy it. What you will want to do is powerwash or scrub/rinse the rock as good as you can. Be diligent. Then, make a very strong bleach solution in a large tub and stick your rocks in. Leave them there for 8 hours or so and remove/rinse thoroughly. Fill the tub back up with clean water and add plenty of Prime, then put the rocks back in. Let soak for 8 hours. Remove rocks and let air dry in direct sunlight outside for 8 hours or so. The rocks will be bone white and very attractive by this point.

You can use the holes sorta like wabikusa and put anubias and other rhizome type plants in them, will look excellent and you will not have to worry about the Victorians digging them up out of the substrate.

edit -- I also had black beauty substrate in my cichlid tanks. The white rocks give it a really nice contrast.

Last edited by TexasCichlid; 10-30-2012 at 05:59 PM. Reason: .
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post #4 of 7 (permalink) Old 10-30-2012, 04:58 PM
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I like the way a rock sold here as "Mexican moonstone" works for around plants. They are a black river rock that has rounded edges. The shape is nice as it tends to keep the African guys from digging very far. As they remove the sand underneath, the rock tends to slide down into the hole they have tried to dig. They get the idea and go somewhere else. Not very cheap if you buy a tub full but not a big thing for a dozen rocks. I would not worry about them changing Ozarks area water!
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post #5 of 7 (permalink) Old 10-31-2012, 06:00 PM
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Similar black pebbles are sold here under the name "Mexican Beach Pebbles".
Very smooth, rounded rocks available in sizes from about 1" diameter to about 5". VERY expensive! But really nice looking, even when dry, and when they are wet they have a natural sheen that is very impressive. We use them sparingly in ponds and fountains.

Black slate is another option. If you want to build it up in layers, or make caves it works pretty well. Slate is available at rock yards and you might try places that specialize in tile, stone counter tops and similar things.

I got some black rocks many years ago that I would say looks like slate except that they are natural shape, not cut into flat squares. I think it came out of Montana. The rocks I have show a tiny bit of rust, about the size of a dime in several places. This is a very small amount (I have these rocks in a 125 gallon tank) but I would not want to have any more, or use these in a very small tank. I got these at one of the local rock yards.
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post #6 of 7 (permalink) Old 11-02-2012, 01:43 AM Thread Starter
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What about obsidian? I am assuming it is aquarium safe. Since it is a volcanic glass, I would not imagine that it would leech anything into the water. I know you need to watch out for sharp edges, but I would think that I could sand down the sharp edges.
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post #7 of 7 (permalink) Old 11-02-2012, 06:50 PM
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Since you are doing an African cichlid tank, that gives you a lot more leeway as to what is considered 'safe'
Mostly, you really just have to worry about are rocks that may contain toxic compounds (avoid metal ores, etc.)

Usually when people are concerned about rocks, it's for a more typically softwater tank, and a lot of rocks will raise the pH and the water hardness. But with African cichlids (and marine tanks) this is actually beneficial.

Anyways, Obsidian should be perfectly safe in terms of chemistry (for soft water tanks as well). Most volcanic rocks are pretty inert.
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