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Discussion Starter · #1 ·
Anyone know what kind of rock this is and if it's inert? On certain faces it looks like pumice but on others it doesn't have the same porosity. If I break it in half, the inside is porous just like pumice. The rock itself is very light and it's quite brittle.

Thanks in advance!
 

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It looks like a black lava rock.

Bump: Clean it up real good and you should be safe. I suppose the smooth part was exposed to the air while it was still molten and the inside had many trapped gas bubbles that slowly dissipated after it cooled. Good place for ferns and moss to grab ahold of and shrimp will like it.
 

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Discussion Starter · #4 ·
Appreciate the responses! I thought it might be pumice but every time I do a Google image search for pumice rocks, they look round and completely porous instead of like these.

I have used them in past tanks before but those tanks had some Sakuras that died within a month, so I'm trying to determine if these rocks affected the water parameters at all (pH out of the tap here is high but within reason for neos). Lava rock and pumice are supposed to be inert, correct? I'm wanting to use these for some new shrimp tanks.

Those tanks had some Cory habrosus that did just fine, tho they didn't really sit on the rocks too much. There are definitely some sharp edges tho.
 

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It does look similar in appearance to Feather rock and your comment that it also floats leads me to believe that is what it might be. It is rather abrasive but I have had no serious fish damage using it in my aquariums over the years.

In order to get it to sink, I've either boiled it in water or baked it in the oven at 200F and then immediately dropped it in a bucket of water. Both methods worked and I've never seen the rocks explode using either method. I used a huge turkey fryer for the boiling method, outside use only, for larger pieces; the oven method does stink up the kitchen a bit for a couple hours.

I have also used it in red cherry shrimp tanks with no problems.
 

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Discussion Starter · #6 ·
Wow I'd never heard of feather rock but some of the image search results I get are pretty much right on the money!

It actually doesn't float but it is fairly close to being that light. Good tip about baking and then immediately throwing in water to absorb as much as possible.

Gonna try these rocks again in a shrimp tank then. I believe I've identified the reason for the shrimp deaths and it definitely doesn't seem like the rocks.

Thanks again everyone!
 

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Where did you get this from? Being from a family with metal workers, I've been familiar with slag far longer than lava rock. Google some images of slag and take a look. It's a byproduct of smelting that can look very similar to lava rock but contain lots of stuff you'd not want to put in with your aquatic stock.
 

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Discussion Starter · #8 ·
Hmm slag looks pretty on-point too. I got this from an LFS maybe 3 yrs ago. I just went to that LFS yesterday and they no longer sell it. What kinds of things go into slag that make it unsuitable for aquarium use? The LFS owner is apparently a pretty hardcore hobbyist so I would think he knows what he's selling, but perhaps he learned something along the way that has brought him to stop selling the stuff.
 

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You'd be better reading a bit on it yourself, but basically it's what's left over when raw iron is smelted and/or converted to steel. Depending on the desired end product it could have other things added to it, but it will consist of anything left over from the base material after the iron/steel has been taken out. Here's some basics on it:
Chemical characteristics of iron and steel slag : NIPPON SLAG ASSOCIATION
 

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Discussion Starter · #10 ·
Interesting read, thx. I had these rocks in a tank for 1.5 yrs and the P. simulans were fine the entire time, not really sure if it was the cause for other fish/invert deaths tho. I believe there are substrates out there made of coal slag; could it be possible that this rock is coal slag?
 
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