Rusty Colored Rocks Safe?

Bought all these at a place that sells yard rocks. I think its slate or shale, not sure. Its for a cichlid tank. I love the look of the rocks but as you can see a lot of them look rusty. Just would like to know if they looks safe before I start adding fish.

 

Give them a good wash off in super hot water, dry them off, and put a couple drops of vinegar on. If it fizzes - bad. If it does nothing, rinse them off again to make sure they won't discolour your water, and you're good to go.

 

Personally I test all my rocks with Muriatic acid from any home hardware store, its very cheap for a small bottle and last forever. If you see any bubbling don't use them. If you search the internet with Safe Aquarium rocks you get all kind of info.

Shale, the softer relative of slate, can sometimes present an unusual problem. Some shales contain a high percentage of organic matter. Even if they are hard enough not to crumble underwater, such shales can release hydrocarbons (petroleum) into water which will collect as an oily scum on the surface. Clearly, you do not want oil-shale in your tank. Most shale does not present this problem, but it is worth bearing in mind when you inspect water that rocks have been soaking in.

 

Agreed. Check this video I constantly reference. Some times the measly 5% acid in food grade vinegar isn't enough to show a reaction. Use muriatic carefully. It can burn.

 

Personally any rocks I use from outside I will boil for at least 15 minutes, you never know what micro organism is living on the rocks.

 

Be careful with boiling rocks. Some types have gas pockets that will expand as they heat and can even cause the rock to explode...

I've never seen it happen from boiling water, but have had it happen to rocks in a fire pit. Usually they just break in half but I've seen them explode hot coals everywhere. Maybe keep a lid partly on the pot just in case.

 

I did the acid test. Did not fizz. Water is clear. Hopefully they are good! Thanks.