On Thu, 2 Aug 2007 07:41:02 CST, "RichToyBox"
wrote:


"DavidM" wrote in message
...
RichToyBox wrote, On 30/07/2007 13:52:
There is another test out there that is more beneficial, called KH
hardness.
The KH test measures the bicarbonates in the water. If the bicarbonates
drop low, then the pH becomes unstable and will crash to very low
numbers. The bacteria use bicarbonates in there changing ammonia to
nitrite, and nitrite to nitrate. The bacteria actualy produce acids that
must be neutrallized for their health and the health of the fish. The
bicarbonate ion is easily changed by the acid to CO2 and water. It can
also neutralize the hydroxyl (very alkaline) ion, by being converted to
water and carbonate ion. The carbonate ion will combine with the calcium
in the system and make a relatively insoluble balance limestone like
material. The KH needs to stay above 80, and it doesn't hurt a thing to
have it stay above 300. The balance between bicarbonates and carbonates
occurs at a pH of 8.3 to 8.4. To raise the KH add baking soda.

Would acid in the water act on chalk in the same way? Could a lump of
chalk be used as a slow release aid to buffering?


--
DavidM
www.djmorgan.org.uk

Yes. The pH would have to be much lower to dissolve the calcium carbonate.
Many wells have water that has been through limestone deposits and when it
comes out of the well, it is at a pH of around 6. After aeration, it will
jump to around 8. What is happening is the CO2 is being outgassed. I am
not sure of the KH out of the well, but the water will generally have a high
GH from all the calcium ions from the dissolution.

The geologists use hydrochloric acid to distinguish between limestone Ca2CO3
and dolomite CaMgCo3. limestone will foam from rapid dissolution, while
dolomite will not. Dolomite is much slower dissolving. There are many
forms of calcium carbonate, which include limestone, dolomitic limestone,
chalk, marble, and oyster shells. Marble has been cooked under high
pressure and because of its density is much less soluble. The finer the
material, the more surface area, so the faster it can react, so pulverized
will work, but it will make a muddy mess when it is added.

Minor quibble: "Chalk" is often gypsum, or calcium sulfate, rather
than calcium carbonate. It is not uncommon, however, to find gypsum
speleothems (cave formations) in calcium carbonate caves. Likewise,
it is not uncommon to find caves developed in gypsum.