Some people use the vinegar method, I think; leave a piece in a glass with some vinegar overnight, and if the vinegar's cloudy or there's residue on the glass than it's something that will eventually dissolve into your aquarium and screw with the PH and all.
If you're talking about about rocks from outside, though, it'd be easiest to just take a look at what kind of rocks are most common in your area. For instance, out here there's nothing but limestone, which will dissolve and make the water hard. no point in doing a vinegar test; nothing from my yard's gonna pass.
say you're in an area with something else, then it might be worth it to test some rocks.

Personally, I just bought a bag of river stones from the craft store and boiled them for an hour to sanitize them. I haven't had any issues, but they've only been in there for a day.

 

I get river rocks from the dollar store too. Never had any problems. Make decorations and stuff with them.
It's like... a dollar for a pound or two at the dollar tree. Least it feels like that much. xD

 

My sister used the viniger method but she also boiled them and they are doing just fine in her 40 gallon... she has had tem in there for about a month.

 

Never boil a rock! There have been instances where rocks explode while being boiled.

 

I found this article to be helpful when I was searching for rocks to use in my desert themed aquarium. I just found a few rocks the other day but I actually need to pick up some vinegar to test them still. First I would scrub the rocks and get any dirt off them. You can boil the rocks after they pass the vinegar test, or at least let them sit in (chlorinated) tap water for 24 hours to kill any bacterias and things on them.

 

Thanks for all the input!

 

You don't have to submerge the rock in vinegar. Actually, vinegar is a poor test because it is a weak acid.

There are a couple of things to keep in mind when thinking about adding rocks to the aquarium.

One is whether the rock contains any heavy metals. This is difficult to test for, so if you know what type of rock it is, that helps.

The second is the more common issue, which is adding a rock that contains a high level of carbonates. Carbonates dissolving into the water will make the water harder, and can cause issues over time (depending on the concentration of carbonates).

There are two different reliable tests for carbonates that you can do at home:

1. R/O leech test
2. Acid test

The R/O test is easy. Dump some R/O water into a clean bucket, and run an airstone in it for an hour or so. Test the pH of the water and record it. Drop the rock in. In a week, test the pH again. If it has changed, the rock is altering the water and shouldn't be used.

The acid test is easy as well, depending on what you have on hand. Vinegar that we generally keep in the kitchen can be used in a pinch, but it's a weak acid. Dribble some of it onto a clean, dry rock. If it fizzes, the rock is unsafe. A stronger acid is better, like hydrochloric acid (also called muriatic acid). If you want to, you can pick up muriatic acid in the solvents section at Home Depot. However, if you have an API water test kit like most of us do, the Nitrate #1 bottle contains hydrochloric acid. Squeeze a couple of drops onto the rock, and watch for fizzing. If it fizzes, don't use it. If it doesn't, you can wash it off again and use it.

If you need to sterilize a rock (and I recommend you do), soak it in a bleach solution for a while, and then rinse with clean water, then soak in regular water tht has been treated with a double dose of water conditioner. Then rinse it again, and soak again with the conditioner before adding it to the tank. Never, ever boil rocks!

 

Yeah I read up on the internet not to boil rocks but just wanted to hear other peoples opinion as well. Once again thanks for all the advice!

 

not sure what boiling does in terms of killing things. i did submerge my zebra rock into very hot water (close to boiling) for 5 minutes, turn off the gas, let it sit for several hour until it cools off. I have not put it in the AQ yet, will try Tekkguy's recommendation just to make sure.