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Re: Hardness and plants (was A PD V3 #727)
Hello Dave,
You write:
> A couple of remarks have appeared on this list lately that I fear > may be confusing to tyros. Some folks have intimated that "hardness" > is bad for plants. First, I am not an authority on this subject so > I used the Tropica catalog as a reference. Second, European water > is ofter VERY HARD, so when Europeans say hard they mean something > like OK or West Texas. Where a teapot lasts a week before it fills > up with CaCO3 deposits. These remarks also apply to those who are > concerned about using a substrate containing shell fragments for > planted tanks. I will not address the needs of fish here. Some fish > DO require soft water.
>
> That said, hardness is a blessing. Hardness comes in two kinds, > permanent and temporary. Chemists, forgive me, I know this is > obsolete terminology. But I am trying to deal with whatever folks > may conceive hardness to be.
You are forgiven! This terminology is as valid today, as it was 50 or 75
years ago. Today we have better analytical techniques to measure them,
but the "nature of the beast" has *not* changed at all!
> Permanent hardness is ordinarily a sign of calcium in the water > (sometimes Magnesium).
(snip)
> Temporary hardness is permanent hardness plus transient hardness.
> Transient hardness is often due to CO2, another serious nutritional
> requirement of plants. It is not necessarily bad.
In 99% of the cases Water Hardness is due to calcium/magnesium salts.
Because calcium and magnesium are chemically very similar, they are
usually lumped together. This -- calcium & magnesium -- is what the
common "Hardness Kits" measure.
*Temporary* (or transient) hardness is due to carbonate and/or
bicarbonate salts of calcium and magnesium. It also contributes to the
*alkalinity* (also called "carbonate hardness", "KH" or "dKH").
It is called temporary hardness, because it *can* be removed by several
simple means (such as boiling, addition of Ca(OH)2, etc).
*Permanent* hardness is due to all other salts of calcium/magnesium.
Usually it will be chlorides and sulphates, but, particularly in the SW,
it is not limited to them. Most testing kits do not measure permanent
hardness separately, but include it in Total Hardness.
*Total* hardness is the *sum* of permanent and temporary water hardness.
In practical terms it is the amount of calcium and magnesium present in
the water, *expressed* as CaCO3 (calcium carbonate) [or, in Germany, as
CaO, calcium oxide]. It is often abbreviated "TH", "GH" or "dGH".
*Carbonate* hardness is actually NOT water hardness at all, but the
measure of alkalinity of the water. In European waters it is often
*equal* to temporary hardness, hence the (incorrect) use of the term
"carbonate hardness" for alkalinity.
I agree with you, that moderately hard water does no harm to plants.
Without *some* magnesium plants could not produce chlorophyl!
Wishing you Merry Christmas and a Prosperous New Year!
Best,
George