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Re: Aquatic Plants Digest V3 #284

Hoa G. Nguyen wrote:
> I recently traded in some plants for some fine-grained Cambria 				> gravel that I wanted to add to my aquarium.  I tested it with 				> Muriatic acid and it fizzed a lot though, so I know that it 				> probably will raise my pH. I am thinking of soaking it in diluted 			> Muriatic acid to produce a "neutral" gravel. My questions are:
> 1.  Will this work?

I am not certain what exactly you mean by "Cambria gravel", but assume
that it is a mostly non-carbonaceous rock (the fizz comes from
decomposing carbonates). If that is so, then treatment with muriatic =
hydrochloric acid will dissolve most of the accessible carbonates and
leave the other components (silicates?) in place.

By the way, any mineral that contains soluble carbonates will, as you
correctly surmise, raise your pH but if it contains calcium carbonate,
it will, over time, also increase your water hardness.
> 2.  Are there any bad, toxic by products (gas or otherwise)?

Hydrochloric acid is a gas. Dissolved in water it is commonly sold as
"muriatic acid" for treatment of concrete. During any reaction,
particularly one producing bubbling, some of the gaseous acid in
solution will be in the "fumes". Breathing air which contains HCl is NOT
a good idea - it can give you edema. The other gaseous product - carbon
dioxide - is essentially harmless at low concentrations.
> 3.  What are the chemical reactions?  Where will the calcium go?

CaCO3 + 2HCl = CaCl2 + H2O + CO2

Calcium chloride [CaCl2] is very soluble in water, so it will stay in
solution and be washed away.

As a practical approach try the process on a handful of gravel, wash
well, dry, and then add some more acid, to see whether your treatment
removed all the carbonate. If it fizzes again, I would not use it where
neutral gravel is indicated.

Hope this helps.