Hi all,
Hate terms such as kH & gH, always have to look them up. Much prefer ppm and the substance of interest. Terminology also muddied by assuming all waters are natural and using Ca2+ as an industrial short hand
It would make a lot more sense.
My question is this: It seems to me that KH should be kept high if you want pH stability since this is a buffer. However low GH and KH seem to be what a lot of people are aiming for. I do not really get that. Why would you want to remove something which stabilises your pH?
That is it. The carbonate hardness (which we use dKH as units for) stabilises the pH at ~pH 8 via the CO2/carbonate equilibrium (assuming ) 400ppm atmospheric CO2. The total amount of inorganic carbon (TIC/DIC) remains the same, it form just changes dependent upon pH. When you add CO2 you depress the pH, because you've added H2CO3, and that is a proton donor (the "spare" H+ ion).
If you keep hard water fish (lake Tanganyika cichlids etc.) or hard water plants (
Vallisneria etc.) they have evolved in carbonate rich water and have adaptations for this environment. Plants like
Vallisneria etc. have the physiological pathways to use bicarbonate (HCO3-) as a carbon source in photosynthesis and to efficiently sequester nutrients like PO4 --- and Fe+++, which are of very limited in their availability in hard water. They also often don't have any mechanisms for avoiding iron toxicity in reducing or acidic conditions.
The pH stability of hard water isn't as set in stone as many people suggest, mainly because <"
in vegetated water there will always be diurnal swings in pH"> caused by the differing CO2:O2 ratio during (and after) photosynthesis. In carbonate buffered water the amplitude of the swing will be much reduced.
Most commonly kept fish and plants don't have any particular water requirements, and will live and reproduce in a range of water types. In very hard water a lot of plant nutrients are less available and high levels of Ca++ ions may interfere with the uptake of Mg++, Fe+++ and K+ ions, and bio-calcification.
A limited number of plants and fish come from water without any natural carbonate hardness, this includes many of the "black-water" fish from SE Asia (
Parosphromenus spp.) and the central Amazon basin (
Dicrossus filamentosus etc.), and plants like
Syngonanthus &
Tonina and
Brasenia species. These plant and fish can only be maintained long term in soft, acid, nutrient poor water. The exact reason for this is not fully known, but may relate to their efficiency in obtaining scarce cations in their natural habitat, and problems with an excess of these elements when they are more available.
Does any of this matter? <"
Views on this forum vary">.
cheers Darrel