"Margolis" wrote in message
...

You keep saying that having these other phosphate buffers is not normally
the case in an aquarium. But it seems to me that the reality is it is more
common than not. Most people don't run RO water with just the proper
minerals added. Most people start with tap water and then add phosphate and
other buffers to it to dechlorinate it and alter the ph to what they think
it should be. Not to mention all of the water treatment facilities that add
phosphates to the water.

Hmmm... I don't know many tanks with phosphates above 1ppm. And, at
that level, the phosphates don't distort the CO2 chart to any noticeable
degree.

Then you have the people that see these charts and think all they have to do
is lower the ph to raise the co2 level. So it is safest just say the chart
isn't accurate unless you are adding co2, imho.

Ah, OK, I'm with you now -- I agree. The KH is a constant for the purpose
of this discussion, and the pH is the result of the amount of CO2 in the water,
that is, the CO2 is the *cause*, and the pH is the *effect*.

I agree that, if people think they can lower the pH to get more CO2, they are
misguided. The *only* way to get more CO2 is to put CO2 into the tank.
Products that otherwise tinker with the pH to artificially lower it (such as
"pH Down"
and similar) don't do a thing to the CO2 level. And, if such products are used,
the
chart will indeed be way off.

BTW -- any artificial manipulation of the pH level with acids or bases is
generally
a bad idea because it can lead to a very unnatural ion balance. The pH is the
result of the level of carbonate hardness, so the best way to target a
particular
pH is to raise the KH by adding calcium carbonate, or to lower the KH by
diluting with RO water. If the GH in degrees is roughly the same as the KH,
then
the ion balance in the water is generally OK too.

If you aren't adding co2,
then you don't need the chart, since you won't have more than 2-3ppm of co2
anyway ;o)

Ah, yes :-) Actually, according to Krause, the equilibrium level is closer to
0.5ppm.
But the precise figure is academic, I suspect, because 0.5ppm and 2-3ppm are
very
nearly the same when it comes to growing plants: too little.

Cheers,

Michi.

--
Michi Henning Ph: +61 4 1118-2700
ZeroC, Inc. http://www.zeroc.com