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Risks of wild caught rocks?

BF McUmber

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Hello all, 

I went to our local river and was able to pick out some nice rocks for my new tank setup. In cleaning them, some of the rocks have cracks/holes in them,  others look like they have different rock deposits in them that look almost sandy, and other allow small particles to be rubbed off.  I can get some pictures tomorrow when it gets light out outside. I have varying colors or reds, whites and blacks that see like they will work well together. In watching videos a lot of people focus on the acid test to see if it will change water hardness. It seems like regardless of the rock type there are three main concerns:

1. The rock can dissolve in your tank increasing the hardness of your tank. I am not too concerned about that one right now. 

2. The rock can have copper deposits in them that can kill your invertebrates. It can also have iron too. This can be seen by the green or brown rust on the rock. 

3. The mud and little cracks in the rocks can harbor wild flora and fauna that we do not want in our tanks. This can be treated by bleach, boiling rocks, or baking them. Thin or deep cracks look cool but could be hard to get cleaned out. 

Besides the copper veins being a big issue for my shrimp it does not seem like the others are deal breakers. Is there other thinks I should be considering before I put the rocks in my tank as hardscape? How do you feel about wild caught rocks?  


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Depending on the rock, it can change your hardness, KH, and/or pH. I don’t consider the acid test super accurate in terms of determining if a rock is definitely inert. If you see fizzing, the rock is definitely NOT inert, but if you don’t see fizzing, that means it could be inert or not.

Depending on the project, I’ve been known to just toss rocks in with the fish and see what happens. But if you really want to test it, get your rock and two identical tubs or jars. Rinse and scrub the rock really well, then put the rock in one container, and leave the other empty. Fill both containers with water, and test periodically for two weeks. You’ll be able to see if the rock significantly changes the water chemistry by then.

Another helpful thing is to look up the type of rocks that can be naturally found in your area. I learned that my area is mostly sandstone, so I can be pretty confident that rocks I find are sandstone. Limestone is commonly used in construction, under patios, etc, and it will raise your KH and pH. I have that in the dirt around my house, and I’ll use it in some tanks where I want to harden the water.

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