hello. Vinegar test on rocks

[fred the fish]

Hello. I'm new to fish. A friend got me a betta and a small aquaponics tank to grow microgreens but I know nothing about either. (I've set up a 10 gallon tank for him that's cycling. For now he's in a 3 gallon tank.) I've been perusing different forums and reading articles to try and learn. This is much harder and more complicated than keeping other kinds of pets.

My question is about rocks. I have many various rocks that I've had for years. I poured boiling hot water over some of them and tested them with vinegar before adding them to the 10 gallon tank. I have another small aquaponics tank that I'm setting up for some small fish or shrimp. I'm testing a couple of rocks to put in this tank with a piece of mopani wood. When I poured the hot water over the rocks, some bubbles came up. In one rock the bubbles continued until the water cooled and then stopped. The other rock had a few bubbles but they stopped after a minute or so (I think that rock is some kind of slate because of the structure, but I also know nothing about rocks. I have no idea what the other one is but it doesn't look porous.). I'm still going to do a vinegar test, but my question is, if the vinegar test looks ok, should I use them? I'm concerned about the bubbles. I've seen contradictory advice in different places. Any advice would be greatly appreciated. I've added pictures. It's the bigger rock I'm more worried about. There are some noticeable cracks in it. Thanks!

 

[Aiken Drum]

Boiling rocks is very dangerous. Air pockets inside the rock expand, and the rock can explode. Don't pour hot water on rocks or boil them.

The bubbles are just air inside the rock escaping. Nothing to worry about. All the vinegar test will tell you is if there are minerals that will disolve and may effect your water hardness and pH, and that may or may not be harmful, depending on your tapwater parameters and the fish you want to keep. That doesn't tell you anything about whether the rocks are safe or not. They might contain copper which will kill inverts, slate can contain copper. Unless you are knowledgeable about geology the only way to know of its harmful is to try it.

If your rocks bubble with vinegar it tells you that they may partially disolve. Some fish prefer the higher mineral content this causes, and if your tap water is already high in disolved minerals it probably won't disolve any more. Just because it "fails" a vinegar test doesn't necessarily mean you can't use the rock, it just gives you a clue as to how it will effect your water chemistry.

 

[fred the fish]

Thank you for the input. The water here is very hard and alkaline so it has a lot of minerals in it. I was surprised to learn that our water is alkaline because I always thought otherwise.

Is there an easy way to test for copper?

Thanks!

 

[Aiken Drum]

You can get a water test for copper, but you would need to put the rock in water and give it time for the copper to get into the water, which could take months.

If you want to know what's in the rocks you would be better off talking to geologists. But you mention slate, and slate will have veins of various minerals running through it depending on what else is in the ground where it's dug up, and that can include copper.

Copper can get into water from all sorts of sources. It will be naturally in your tap water, come from your water supply pipework, and hot water cylinder or your boiler. If your water is hard and higher pH, then it's not going to be very reactive and the rock probably won't change the water chemistry very much. Your water company should be able to give you a full report on whats in it, or if you are on a well do you get regular water test checks? The easiest way to say if the copper content is too high for inverts is to get a few shrimp and see what happens over a few months.

If your water is very hard and full of minerals the mineral content may be too much for shrimp to do well regardless. Its common for shrimp to have trouble moulting if the calcium content is high. Do you know your pH and general hardness?

You mention you have had the rock for a while, but not where you got it from or what it's been used for? Might it have been somewhere where it could have picked up chemical contaminants like petrol chemicals or pesticides etc?

 

[fred the fish]

I'm getting an API test kit shortly. So far I've just been using strips.

I honestly don't remember exactly where I acquired all the different rocks. I think I got the larger one in California, near Modesto, at a park in the mountains. It was in a stream. This was years ago, in the mid-90s. Not exactly sure where I found the other one, maybe in Austin, Texas. I did collect a bunch of rocks when I was there.