are these rocks safe for freshwater planted tank? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 03-19-2013, 10:48 PM Thread Starter
Algae Grower
Join Date: Feb 2013
Location: Bay Area, CA
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are these rocks safe for freshwater planted tank?

*moved my thread*
just came from tahoe and i picked up a few rocks that i would like to use in my 55gallon tank. currently have flourite dark as my substrate and will be planting some DHG to do a carpet. i want to make sure these rocks are safe for my tank, any info would be apreciated. im not planning on using all the rocks, just a few to kinda lay around my tank. it will be community tank.

1.all rocks have been scrubed and rinsed, both groups have soaked in hot water for about 2 hours.

2. poured a little vinegar on the rocks, no fuzzing. i did get something that looking like fuzzing but i think it was just the vinegar going into the rock.

3.3/18/13 i have group 1 in a bucket of water now, going to let them sit there for a week to see if they change the is what my water looks like from outside.




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post #2 of 6 (permalink) Old 03-20-2013, 03:05 AM
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Well, my husband (geology minor in college and lifelong rock collector) says those are probably sedimentary rock (most likely sandstone) and could possibly break down or leech minerals into your tank. You do have some fossils in them, though!
Limestone is the rock that fizzes when splashed with vinegar. You don't want that either. Ultimately, it depends on your water chemistry and your own personal comfort level. If your pH is already 7.6 it might not matter much.
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post #3 of 6 (permalink) Old 03-20-2013, 03:33 AM Thread Starter
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ahhhh i see, ty so much for the info. well i dont plan on using all of them, i was actually thinking of breaking down a few of the big ones and laying them out. the rocks didnt actually fizz when i poured vinegar, it seemed more like it was traped air coming out of the rock from the vinegar entering the holes (if that makes any sence) lol my tank right now is at 7.0

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post #4 of 6 (permalink) Old 03-20-2013, 03:17 PM
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I would do a chlorine test. Fill in 1/2 of a 5 gallon bucket. Dump one rock of a time. If it fizzes, don't use the rock. To dechlorinate the rock, you can either sun dry them for a few days or dump in a 5 gallon bucket filled with water and 5X the dose of a dechlorinator like Prime.

I have used rocks this way with no problems whatsoever. The first poster is right, some sandstone is ok for the tank, but may still dissolve under water over a few months.
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post #5 of 6 (permalink) Old 03-20-2013, 05:49 PM
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First of all, the vinegar test is not very reliable. It's better to use a stronger acid if you can, and scratch a bit of the rock up; and even then it's not always apparent. All it does is reveal whether there are carbonates in the rock (acid reacts with carbonates, releasing CO2). For example, dolomite is hard for a lot of people to identify on mineralogy tests and what not, because it rarely fizzes, even when using a stronger acid. I doubt it would fizz at all with vinegar. It can still be a useful test, just keep in mind that it's a test prone to false negatives.

Another test that can help is to scratch it with a piece of steel (a nail, knife point, etc.). If you can't scratch the rock, it's probably some sort of silicate (very gross generalization) and may possibly be safe (big if). If you can scratch the rock with steel, it's not necessarily unsafe, but most of the rocks that will affect pH/hardness are going to be on the softer side of the Moh's scale.

The first group looks like it might be some sort of breccia. It's going to be tricky to say much more then that, since it's composed of a bunch of smaller individual rocks and a matrix, all of which can have very different mineral contents.

And, I've got nothing on the second group...
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post #6 of 6 (permalink) Old 03-21-2013, 12:50 AM Thread Starter
Algae Grower
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Location: Bay Area, CA
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yeah i think the first group wont be safe since it is a bunch of smaller rocks combined, im gonna cut up the second group and use smaller sections to see how it goes, im gonna use about 10 small 2-3" rocks for my scape from group 2

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