Marble and Natural Stone

[Alaris]

Is marble ok to put in a tank? (That is not marbles as in the toy, but marble as in the stone.) Also what about other natural stone such as jade?

And how about found rocks? My brother-in-law found some nice large river rocks in a creek near his house and put them in his tank. (I don't know how he treated them if at all - wouldn't surprise me his tank in not-so-good condition.) Anyways, the rocks are cool and my husband wants to put some in our tank. I assume this is ok and of course the rocks need to be rinsed, but do they need any other treatment?

 

[JohnPaul]

When using natural stone, there are two things to be concerned about:

1. Nasty microorganisms hitching a ride on (or inside the pores of) the stone and then infecting your fish.

2. The stone causing changes in pH.


As for #1, that means you want to sterilize the stone before you put it in your tank. If it is a fairly nonporous stone, I would think a 10 or 20 minute soak in a 1:20 bleach solution would do the trick. If the stone is more porous and you are worried about bugs being deeper "inside" the stone, then a good 20 minutes in boiling water would be the other option. Note that if you do the bleach option, not only do you want to rinse the rock off really well, but after doing a half dozen good rinsings or so, soak the rock overnight or even for a few days in a bucket filled with a triple dose of your water dechlorinator...just to eliminate any last traces of bleach from the pores of the rock before you put it in your tank.

As for #2, there is an easy way to test for this. Take your stone (dry, not wet), and drop a few drops of vinegar on it and then observe very closely. If you see any small bubbles forming, that tells you the rock is some sort of a carbonate-based rock, which will slowly leach carbonate into your system and raise your pH if you put it in the tank. How much it will raise it depends upon how large the rock is and exactly what type it is. If you have a specialized high pH tank (cichlid tank, Sulawesi shrimp tank, etc.) that extra alkalinity is no biggie. However, if you have a small tank you are trying to keep at acidic or near-neutral pH, having a big chunk of limestone or similar rock can potentially bump your pH significantly higher than you might like it.

Marble is primarily crystalline calcium carbonate--so it is one of those things that will do this. Jade I'm not sure about, you'd have to test it and see.

 

[Purrbox]

Sometimes the vinegar test isn't 100% accurate. If the amount of carbonate is too low it may not react witht he vinegar but still affect your KH/pH. If there are strips of different stone you don't test all areas, one of the ones that wasn't tested could affect the water as well. A much more sure fire way to test is as follows.
Fill a bucket with water and either let it sit for 24 hours or aerate it for an hour to get rid of any dissolved gasses. Test for pH/KH/GH. Add the rocks and test again a few days later. Any change in the test results indicates that the rocks will affect the water chemistry.

 

[jsoong]

But if your water pH is already 7.8 or 8, then you don't have to worry about carbonates dissolving into the tank .... that is near saturation pH for CO3.

 

[Alaris]

So basically the main problem with adding marble and stone is that it could raise my ph? Other than that it's not going to be toxic to my tank?

And on found rocks I will definitely clean and/or boil them for bugs.

Thank you.

 

[Purrbox]

In most cases, yes. Sometimes you'll find rocks that have mineral deposits which can be problematic. Copper for instance is not good when you want to keep inverts.