Thusly "RedForeman ©®" Spake Unto All:

Calcium carbonate is an additive, mainly used for reef tanks, helps keep the
corals and shell animals healthy, and no, it's not actually a buffer... what
*is* a buffer is sodium carbonate..aka.. baking soda.. Arm&Hammer....

Calcium carbonate is an almost insoluble solid, aka limestone.
Bicarbonate is the same as KH, although in marine water carbonate
matters too.

Limestone, when subjected to any pH below about 8.3, will dissolve
into free calcium ions and, yes, bicarbonate. So limestone is a
buffer, just not a fast-acting one, as it's a solid with poor
solubility, but it will dissolve, and it will buffer pH. The
solubility of limestone is pH dependent, so at very low pH it will
dissolve relatively rapidly (try dropping acid on a limestone),
whereas at pH's above 7.5 the dissolution is so slow as to make no
difference.

Baking soda (which, incidentally, you should make sure is pure sodium
bicarbonate and not added with biphosphate and starch) is sodium
bicarbonate, and easily soluble. That means that it instantly buffs up
the alkalinity of the water (aka "KH"), and hence buffers the pH.

Bicarbonate on its own will tend to push the pH to 8.3. No matter what
the starting pH, and no matter how much you add, the pH will move
towards 8.3 upon addition of bicarbonate.

The downside with bicarbonate is that, since it is easily soluble, you
can raise the pH *very quickly*, which is not always desirable, and,
since there's no slowly dissolving deposit, the pH can drop just as
quickly when the bicarbonate is used up (converted to carbon dioxide
and degassed or used up by plants directly).

Limestone therefore offer a slower and far more long-lasting way of
shoring up pH, and will also raise the pH to a lower maximum than
bicarbonate will.

To be sure bicarbonate has its uses, but most of the time it's
actually easier to just plonk in a couple of limestones. Or put a bag
of seashells in the filter.

thanks for all the info, i am very grateful!......it is sometimes
difficult to piece together all the bits and pieces available on the
web to make perfect sense, in order to come up with the right thing to
do!

chris

In message , Mean_Chlorine
writes
Thusly "RedForeman ©®" Spake Unto All:

Calcium carbonate is an additive, mainly used for reef tanks, helps keep the
corals and shell animals healthy, and no, it's not actually a buffer... what
*is* a buffer is sodium carbonate..aka.. baking soda.. Arm&Hammer....

Calcium carbonate is an almost insoluble solid, aka limestone.
Bicarbonate is the same as KH, although in marine water carbonate
matters too.

Limestone, when subjected to any pH below about 8.3, will dissolve
into free calcium ions and, yes, bicarbonate. So limestone is a
buffer, just not a fast-acting one, as it's a solid with poor
solubility, but it will dissolve, and it will buffer pH. The
solubility of limestone is pH dependent, so at very low pH it will
dissolve relatively rapidly (try dropping acid on a limestone),
whereas at pH's above 7.5 the dissolution is so slow as to make no
difference.

Baking soda (which, incidentally, you should make sure is pure sodium
bicarbonate and not added with biphosphate and starch) is sodium
bicarbonate, and easily soluble. That means that it instantly buffs up
the alkalinity of the water (aka "KH"), and hence buffers the pH.

Bicarbonate on its own will tend to push the pH to 8.3. No matter what
the starting pH, and no matter how much you add, the pH will move
towards 8.3 upon addition of bicarbonate.

The downside with bicarbonate is that, since it is easily soluble, you
can raise the pH *very quickly*, which is not always desirable, and,
since there's no slowly dissolving deposit, the pH can drop just as
quickly when the bicarbonate is used up (converted to carbon dioxide
and degassed or used up by plants directly).

Limestone therefore offer a slower and far more long-lasting way of
shoring up pH, and will also raise the pH to a lower maximum than
bicarbonate will.

To be sure bicarbonate has its uses, but most of the time it's
actually easier to just plonk in a couple of limestones. Or put a bag
of seashells in the filter.

do they _have_ to go in the filter? I was wondering about raising
hardness the other week, and have put seashells into the tank. My filter
is one of those internals that you stick to the back of the tank (eheim
aquaball) and I'm not sure where i's put the seashells in it...


--
sophie

Thusly sophie Spake
Unto All:

To be sure bicarbonate has its uses, but most of the time it's
actually easier to just plonk in a couple of limestones. Or put a bag
of seashells in the filter.

do they _have_ to go in the filter?

No, you can put it anywhere. But in the filter they're getting better
exposure to the water, hence dissolve faster, hence raise pH/KH
faster.