# What types of rock are okay for tanks?



## PotteryWalrus (19 Jun 2020)

I wish I could say I wasn't a complete noob, but my little 56l community tank is my first in decades and I'm feeling pretty rusty on all this. I'm hoping to just have a nice well planted tank with some shrimp and a small population of endlers. Also hey, I'm Mal XD

The rocks I have the easiest access to are slate, sandstone, granite, and flint. Are these safe candidates for a freshwater tank? And how would I go about washing salt from stones that have been found on the beach?

I should add that I'm doing this on a budget and will probs look hella scruffy compared to your lot,  since all my rocks and wood will be out of the wild XD


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## sparkyweasel (20 Jun 2020)

Slate and granite are good. 
Sandstone if it'd hard, some kinds are a bit soft and crumbly.
Flint itself is OK, but it's often attached to chalk. If your water is soft and acid the chalk can dissolve and make it hard, which you probably don't want, depending on your fish species.
A soak in tapwater is all you need to get rid of any salt, maybe a bit of scrubbing if there's any 'muck'.
If you want to check any unknown rocks (or other stuff);
1; Pour some vinegar on it. If it fizzes, the rock could dissolve in acid aquarium water.
2; Put it in a tub with rainwater, pondwater, or tapwater that's been dechlorinated (either by aging or with water conditioner). Add a few daphnia and/or cyclops. If there's anything harmful in/on the rocks the daphnia will soon die off.


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## JoshP12 (20 Jun 2020)

sparkyweasel said:


> 1; Pour some vinegar on it. If it fizzes, the rock could dissolve in acid aquarium water.



@PotteryWalrus 

I went hunting a few months ago and did this - I noticed that without a magnifying I couldn't see the bubbles from the vinegar. When I switched to muriatic acid (HCl) they bubbled and it extremely obvious what was and was not inert. If you use that stuff, use gloves, perhaps eye gear, and be careful. 

Josh


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## dw1305 (20 Jun 2020)

Hi all, 





PotteryWalrus said:


> And how would I go about washing salt from stones that have been found on the beach?


If you go for rounded cobbles, you can just soak them for a few hours. Only really hard rocks <"form rounded cobbles">, and very hard rocks are impermeable and any salt will just be on the outside.





JoshP12 said:


> I noticed that without a magnifying I couldn't see the bubbles from the vinegar.


If you scrape the surface of the rock with a file  it is easier. If you can scrape up rock fragments then the rock is soft, if it then "fizzes" it is limestone, you have a larger surface area so you have more chance of the vinegar bubbling before it is neutralised. 

If you can't scrape up any fragments then the rock is hard enough that it doesn't really make any difference whether it is limestone of not. 

cheers Darrel


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## PotteryWalrus (23 Jun 2020)

Also I learned yesterday that if you're not sure the rock is fizzing, just put your ear closer to it and you can hear it hiss!


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