Testing rocks

Lukara

Lukara

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Jan 13, 2003
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Hi all. I was reading up on ways of testing rocks and from what I understand, muriatic acid, white vinegar and PH down could be used. Is this correct?

I took a handful of sample river rocks (it was clearly labelled river rocks) today from a home improvement shop and brought them home to test. I rinced them off with water first to clean them somewhat and then I used some PH down and put a drop on each piece of gravel. There was a brief foaming after I applied the drop to each of the gravel pieces. Then later on in the day when I wanted to show my husband, I applied a drop again on the rocks and there was nothing, no fizzing, no foaming, nothing. Does anybody know what this means?

Thanks in advance.
 
Well, I don't know about pH down, but I assume any sort of "fizzing" or "bubbling" is a bad sign. I know that with vinegar, it definitely is not good. You ever do that experiment when you were young with the baking soda and the vinegar?? It is not good for your tank. A lot of people will boil the rocks if they are small enough to make sure there is nothing living on it and that it won't cause any problems. That's as much as I know.
 
A rock that foams with pH down mean there's a likelyhood that it will raise your KH and pH.

As far as your test results, did you test in different spots or on them same spot?

Generally speaking, if you're unsure of the mineral content of the rock and what that might do to your water, you might want to consider sticking with "aquarium safe" rocks from the LFS.
 
You could consult a geology book or look on the internet for minerals in rocks. You basically don't want to put rocks with carbonates and alkaline metals like Magnesium and Calcium in your aquarium.

The fizzing is the carbon dioxide produced when the carbonates in the rock react with the weak acid like vinegar or pH down (phosphoric acid?). Stong acids like muriatic acid (dilute hydrochloric acid), can react with certain metals in the rock, if they are in their elemental states (ie, Magnesium metal).

Essentially the fizzing is an indicator that when the rock starts to dissolve in your aquarium, it will release carbonates raising your KH and buffering capacity.

I put quartz rocks into my aquarium after I did the same tests as you, so quartz is an option. You could also try basalt, obsidian, agate, or maybe granite (not too sure what's in that).

HTH,

Graeme
 
Thanks for the replies. I will not chance it and buy the bag to put in my aquarium. I was curious however to know why the handful of rocks that I brought home didn't fizz the second time. I did try applying the drop on different parts of the rocks also... Anyway, better to be safe than sorry. Thanks again :)
 
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