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Re: [APD] Re: PH and CO2 questions

On Tue, 02 Dec 2003 21:31:55 -0700, Chuck Gadd <cgadd at cfxc_com> wrote:

Clint Brearley wrote:

Tarah Nyberg wrote
However, In order to reduce the net amout of CO2 that you need for you
plants you can also reduce the KH. at a KH of 2-3, (36-50ppm) you will
need much less CO2 to keep your plants happy. I don't have the chart
handy, but this should be evident from the chart.

What? This doesn't make sense to me. Why should the KH have any influence
> on how much CO2 the plants need? Lowering KH will just lower pH (if CO2
> stays contstant) but have no effect on CO2 or the plants CO2 requirements.

You are exactly correct Clint.

Regardless of what your KH is, you need to inject the same amount of
CO2.  Changing the KH only changes the pH at a given CO2 level.  And
we know that pH isn't what's important to the plants.

I didn't think the level of carbonates affected pH, which depends only on H+ ions.
Wouldn't decreasing the KH reduce the amount of carbonic acid absorbed into hydrogen carbonates to form bicarbonates? Thereby increasing the fraction of CO2 left dissolved as carbonic acid and so available to the plants?

Andrew McLeod
thefish at theabyssalplain_freeserve.co.uk
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