Safe Rocks for Apisto Tank

[MikeNYC]

Hello,

I have driftwood, petrified wood, river rocks and natural "pagoda stone" in my 20 gallon SA tank. I am pretty sure none of those will raise hardness or PH.

But, I recenty bought a small piece of lace rock (about 1/2 pound) to put into my 20 gallon. Will this relatively small piece of lace appreciably raise either PH or hardness? I am very concious about keeping PH below 6.6 and the water very soft.

I have heard mixed comments about this, some say it will raise only hardness, some say both hardness and PH, and my LFS said that it is totally safe.

What do you think?

 

[Mike Wise]

Being a former geologist (with a MSc) you'd think I'd know something about rocks. Well, 'lace rock' is a term that is used for many different types of rock. If it is a solid rock with many multi-colored bands in it, then it is probably a rock composed of volcanic ash. This ash is composed mostly of small particles of silica and the rocks formed are either ash fused together (ash flow tuff) or cemented together later by a minerals deposited out of solution from ground water (air fall tuff). The cementing agent usually is silica, but calcite (CaCO3) sometimes can do the job, too. Obviously the ash flow tuff & the silica cemented air fall tuff will not affect hardness or pH. Tuffs cemented by calcite will act just like limestone, raising hardness & pH.

I guess that the best way to be sure that the rock is ok for softwater tanks is to scrape some powder off of the rock & drop some acid on it (vinegar will do). If the powder doesn't fizz it should be just fine. This is a good method for testing any rock.

 

[MikeNYC]

Thanks for that response. Very, very informative.