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Re: Lowering pH when adding hard water nutrients to soft water
To: Aquatic Plants letters <aquatic-plants at actwin_com>
Subject: Re: Lowering pH when adding hard water nutrients to soft water
From: Susi Barber <wanderer35 at operamail_com>
Date: Sun, 3 Sep 2000 18:37:23 -0400
Paul Krombholz wrote:
>My initial thoughts after reading Susi Barber's post about her water
problems is that she should avoid adding any sodium bicarbonate, which
only raises the pH and does not add any nutrients the plants can use.
I reply:
I thought it supplied calcium; I am happy to use an alternative source; or
even none other than the 2.7% supplied in the Equilibrium, and see how
that goes - what do you think? I 'm sure the plants will tell me! Ditto re
magnesium, as it also supplies that. And yes, I am trying to keep it as
simple as possible!
Its sounding like I don't need to add anything to bring the KH up, is a KH of
0 okay, as that is what the water supply has - also 0 GH, and 0 Fe, both
chelated and free.
Also, ditto for calcium: the Lions Bay water doesn't register on my Hagen
test kit, the colour goes deep purple even before I have added any of the
drops to send it purple, and the level for that according to the kit is <20
ppm.
When I add the Equilibrium, I can measure GH, but still no KH or Ca, or Fe
for that matter.
pH varies between 6.4 to 6.8, not sure why - maybe the amount of rain, as
it is coming from a stream??
Paul replies:
When you say, "it supplies calcium", I presume the "it" refers to the
Equilibrium, not sodium bicarbonate. Sodium bicarbonate only adds sodium
ions and bicarbonate ions. My contention is that, since you are concerned
about the pH getting too high, there is no reason to add any sodium
bicarbonate, because sodium bicarbonate raises the pH without adding any
useful nutrients. If Equilibrium has sodium bicarbonate in it, that is an
ingredient you don't want. You want enough calcium to supply your plants
with needed calcium, without getting the pH too high. I see you have a
calcium test kit, and 10 to 20 ppm of calcium should be enough for your
plants. Remember that calcium deficiency shows up in new growth, making it
smaller, distorted, and often streaked with white. More severe calcium
deficiency kills the growing tips of shoots and roots. Your plants also
need potassium, magnesium, and sulfur. You can add these in forms such as
KCl and MgSO4 or K2SO4, without affecting pH.
My tap water has way too much sodium bicarbonate, and no calcium or
magnesium. It is essentially a sodium bicarbonate solution coming out of
the tap with a pH of 8.5. The measured KH is 9.0 and GH is 0. I don't use
this tap water, because all that sodium bicarbonate makes it hard to get
enough calcium in the water from lime or ground limestone. Instead, I use
rain water and add a small amount of lime, about 1/2 teaspoon per 15
gallons. This amount makes the plants happy, gets calcium up to around 40
ppm, and does not make my pH too high. I also add KCl and MgSO4,
micronutrients and chelated iron.
KH is just a measure of buffering capacity of water. It is a measure of
the amount of acid that has to be added to a liter to get the pH down to
four point something. KH can never be totally zero, but pure water only
takes a small amount of acid to lower the pH a lot. One reason you want a
measurable KH is that water with a measurable KH will hold more CO2.
Adding ground limestone (CaCO3 and MgCO3) increases KH because some of the
calcium and magnesium carbonate reacts with additional CO2 to become
calcium and magnesium bicarbonate. These bicarbonates are more soluble,
and the bicarbonate ions increase the KH. With the small amounts of ground
limestone I add, I do not get anything like the very hard water that comes
from wells in limestone regions of the country.
If you add muriatic acid (HCl) to a calcium bicarbonate solution (or sodium
bicarbonate or magnesium bicarbonate) the hydrogen ions react with the
bicarbonate ions, producing CO2 and H2O. The CO2 escapes and you have left
calcium chloride. Your KH drops.
Paul Krombholz, in bone dry central Mississippi