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my mom got flat rocks for her garden and she has a few left. these rocks have a diameter of about 12" and are 3" in height. i planned on putting them in a 120usg that currently has a 10" oscar and a 12" pleco. so knowing my oscar he'll love to try to push over these rocks, but i fear that some how my pleco will be under when he desides to redecorate. so is this a to big of risk to do? or is there a good way of stacking these large rocks?

First off i'de make sure that the rocks are tank safe (won't disolve, raise the ph, leech minerals into the water, etc). After that depending on size and weight I would say silicone glue, and if you're realy concerned try drilling holes in the rock and using some sort of safe pegs to join them as well. I have no clue what you'de use for pegs thats aquarium safe, but if you can find something then try it out.

how can i tell if the rocks are tank safe?

[span class="edited"][Edited by BeastKeeper 2004-07-28 01:42][/span]

I wouldn't do it. Imagine if your oscer is mad and decides to just beat the living $#!? out of your rocks and the rocks tipp over and with the combined weight of all the rocks you glued together it smashes into the side of your aquarium. THat would be a mess to say the least.

I agree with tetraman1225. Oscars are very strong & even if you glue the stones together, they are capable of tipping them over.


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There are two very simple ways to test rock to be sure they are safe for your aquarium. The first method uses Muriatic Acid (MA). This can be found at either a swimming pool supply store or possibly a hydroponic supply store. To test any given rock, put a few drops of MA on the rock, wait a couple of seconds and watch for bubbles. If bubbles are seen, this rock is NOT safe. Distilled white vinegar can also be used in a pinch. The MA test is more accurate though.

One point to remember is some rocks are made up of a conglomerate of differing minerals and smaller rocks. It would be a good idea to test each rock in numerous places. This test can also be used to verify you choice of substrate for compatibility.
Safe Rocks:

Crystalline Quartz
(Rock Crystal, Amethyst, Citrine, Rose Quartz, Smokey Quartz)
Granite
Jade
Lava Rock
Microcrystalline Quartz
(Jasper, Agate, Chalcedony, Sard, Carnelian)
Onyx
Petrified Wood
Quartz
Slate
Unsafe Rocks:

Coal
(Commercially harvested coal is treated with an oil by-product to reduce dust)
Coral
Dolomite
Fools Gold
(or any other rock with metallic veins--Acid Producing)
Fossils
Limestone
Marble
Sandstone

Keep in mind that some of these rocks can be used in some tanks. Crushed Coral makes an excellent substrate for maintaining water quality for African Cichlids. You can even use some rocks that come from limestone to do the same. Limestone will usually do nothing more than raise your water parameters. If you decide to use rocks that will contribute to the overall hardness, make sure you test the water parameters to get a handle on just how high your levels will increase over time.






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good silicone glue is hard for me to seperate by hand if there's a large surface area and its properly applied, if the surface area is low, i'de use plastic pegs. You can also force rocks to stay in place by using big matts meant for cichlid tanks. you stick these things down, tie everything down that you want to stay in place (just make sure the base is good) and throw the substrate in over top. personaly I think there are few reason to ommit something from a tank because of stability- there's allways a way to keep things stable