Re: GH Chanage Over Time

[Roger Miller <roger at spinn_net>]

On Sunday 01 September 2002 01:48, Rachel wrote:

> Since I am never sure I really have this whole GH-KH-CO2 thing down, I have
> a question about the GH part of it. 

It might help if you don't put GH into the pH-KH-CO2 thing.  GH has nothing 
to do with CO2 and GH isn't necessarily related to KH.

> should I see a GH drop using a standard test kit (2 drops
> = 1dH) over the course of a week? I would assume you would, if the plants
> are using the Ca and Mg. If it doesn't drop, then what is the point of
> adding it at all? Is there a lower limit below which the plants can't use
> it?

Plants use fairly small amounts of calcium and magnesium, and dGH are a 
pretty coarse measure of calcium and magnesium levels.  You probably would 
not be able to measure a drop in GH from a week's worth of plant growth.  
Snails, on the other hand, can use up quite a bit of calcium.

Plants use both calcium and magnesium to build organic matter -- calcium in 
cell walls and magnesium in chlorophyll, among other things.  Plants also 
require both calcium and magnesium dissolved in fluids inside the plant.  I'm 
not positive about this, but I think that plants require some calcium and 
magnesium in the water that they're growing in so they can keep the right 
amount of calcium and magnesium in their internal fluids.  That calcium and 
magnesium isn't "used" by the plant, but it still has to be there.
 

Roger Miller