Non-reef rock in reef tank?

[TinnysReef]

Not sure if anyone has tried this, or knows the answer. I've posted questions on the products on BRS's website without response unfortunately.

Has anyone put non "reef rock" in a reef tank? Is it safe? Are there ones that are safe and ones that aren't?

I'm thinking about redoing the aquascape on my Frogfish tank and think it would be cool to build them caves out of boulders. In the tank I mostly have frogspawn and toadstools (get it ... frogfish tank). But thought if I had boulders and had GSP growing on them like moss it could be pretty cool. Posted the ones below that I am interested in. If not, I'll just chisel my Marcorock as usual lol but thought I'd try something different if possible. This one is called elephant skin rock and I think could make great caves.

 

[Dburr1014]

Well, I wouldn't.
Could be iron in that rock among other things.

 

[TinnysReef]

Well, I wouldn't.
Could be iron in that rock among other things.

Dang. Yeah I wouldn't want to risk heavy metal poisoning of any of my critters.

 

[ISpeakForTheSeas]

People have used non-reef rock before - algae seems to be the main concern; while there are theoretical concerns over the leaching of toxic metals, I've never seen any evidence of lethal issues related to the rock:

the leaching is theoretically possible (and may tie in to the increased algae growth discussed below), but, as mentioned below, I've yet to see an example of a tank being unable to sustain corals, inverts, or fish due to the use of lava rock (and I have seen several tanks use lava rock or other "freshwater" rocks successfully for all of the above):

This has been a controversial topic the few times I've seen it come up - long story short, I've never seen a tank crash (i.e. with things dying in it) from the use of lava rock; I have, however, seen lava rock taken from a freshwater setting and reused in a saltwater setting that had major algae problems for about a year (presumably from built up nutrients and/or iron in the rock).

That said, in theory (I've never seen this actually proven to happen in practice), lava rock can leach toxic metals into the water, so to responsibly use it, most people cure it for a decent length of time (several weeks; preferably with RO/DI water because you know it's not adding anything unwanted to the mix).

Given that your tap water has been good enough to be used with shrimp in a freshwater setting and that inverts like shrimp are typically highly susceptible to heavy metal (particularly copper) poisoning, I'd personally assume the lava rock is fine to reuse, but will likely have major algae issues for a while.

Edit: To add one more point to consider: volcanic/lava rock lacks the pH buffering abilities of calcium carbonate rock.

I don't have much in the way of ideas or advice, but with regards to the volcanic rock (scoria rock being the kind of volcanic rock typically used in aquariums): long story short, yes, you can use it (but it's probably not ideal).

People will likely warn you that it could leach toxic metals into your tank and nuke it. This is technically theoretically possible (and there is some slight evidence at this point to suggest that some leaching may happen and cause increased/prolonged algae issues/ugly stage issues - though the instances I have seen in depth info for with this had many other variables at play as well), but I have literally never come across any evidence of this leaching causing tank crashing (or even inverts dying from leaching copper) despite actively looking for it. So, as long as you do watch for issues, you should be fine.

*(In complete seriousness, if anyone has solid evidence of tank nuking happening as a result of the use of lava rock - even anecdotal evidence that just ruled out all or most other potential causes of issues - I would genuinely love to see it; all the evidence that I've seen so far - which involves very few claims of the rock actually crashing the tank - had about a thousand different variables involved that could have caused the crash regardless of the rock.)*

That said, here are a couple of other points that are definitely valid: volcanic rock tends to be sharper/more jagged, and can more easily injure fish (particularly depending on the fish kept in the tank); and volcanic rock lacks the pH buffering abilities of calcium carbonate rock.

And here's a breakdown of the average composition of lava rock just because (scoria is vesicular basalt, so the basalt category would apply to it):

What is lava made of?

Lava is made up of crystals, volcanic glass, and bubbles (volcanic gases). As magma gets closer to the surface and cools, it begins to crystallize minerals like olivine and form bubbles of volcanic gases. When lava erupts it is made up of a slush of crystals, liquid, and bubbles. The liquid...

volcano.oregonstate.edu

 

[TinnysReef]

People have used non-reef rock before - algae seems to be the main concern; while there are theoretical concerns over the leaching of toxic metals, I've never seen any evidence of lethal issues related to the rock:

Thanks! I did receive a frag plug once that was essentially a river rock covered in Zoas so I'm guessing it's possible. But ... do I risk it if there is a chance of metal leaching? Lava rock and this elephant skin rock would be totally different I think as well.

 

[ISpeakForTheSeas]

Lava rock and this elephant skin rock would be totally different I think as well.

Yeah, they're different rocks - Elephant Skin Stone/Rock is a dolomite based rock (Calcium Magnesium Carbonate); unless there's a crazy leaching event (which is unlikely, but if it happens, let me know), the worst I would expect is possibly some extra magnesium in the tank:

I'm not sure exactly what they would be worried about, except possibly magnesium release. According to this paper, dolomite is substantially less likely to dissolve into seawater than is calcite, and we know that calcite is less likely to dissolve than aragonite. That means that to get any dissolution, either the pH or the alk in the pore water around the sand grains would need to drop substantially lower with dolomite to get any dissolution than with aragonite sand.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/sed.12259

"All three source seawaters used in the simulations (modern, Mississippian and Aptian) at 30°C are supersaturated with respect to calcite, aragonite and dolomite"

For what it's worth, Dolomite is frequently used in Calcium reactors in attempt to keep Magnesium levels up as well as Calcium levels.