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Re: Aquatic Plants Digest V5 #84

Gitte asked about use of softened water or reverse osmosis water or lake water.

It all depends on how hard the unsoftened water is.  If it is REALLY heard,
say a GH in the teens or 20's, then the softened water is going to have an
unnecessarily high KH.  Basically, high GH water (lots of Ca and Mg
bicarbonate), will also have a high KH (measure of alkalinity, or how much
acid is necessary to get the pH down to four point something). It is turned
by the water softening process into water that still has a high KH
(alkalinity---now due to sodium bicarbonate), but low GH (no longer has Mg
or Ca). The high KH, low GH water is alkaline, unless you add CO2, and it
doesn't dissolve calcium/magnesium carbonate (limestone) very much unless
you lower the pH with acid or lots of CO2.  High KH, low GH water tanks can
be deficient in calcium, and the plants can develop calcium deficiency,
unless you add lime, crushed limestone or crushed coral (basically all
forms of calcium and magnesium carbonate) etc. AND carbon dioxide so that
the pH will be low enough to get some of the calcium and magnesium into

Water that was quite hard and is now softened is, in my humble opinion, not
improved for growing aquatic plants.  It is only improved for hot water
heaters and the use of soap.  There is a lot more alkalinity due to sodium
bicarbonate than is necessary (some alkalinity is useful for increasing the
capacity of the water to hold CO2), and it only hinders getting enough
calcium into solution to supply the plants' needs.

Our well water in Central Mississippi is naturally softened water, softened
by some sort of geological process.  It comes out of the tap with a pH of
8.5, and has a KH of 9 and a GH of 0.  I got calcium deficiency in my
plants if I did not aggressively push calcium with the addition of lime or
some form of calcium carbonate, such as ground up egg shells or ground
limestone along with enough CO2 to get the pH into the 6.5 to 7.0 range.  I
have switched to rain water, and I get the GH (and KH) up to the 5-10 range
with additions of lime.  The well water had no advantages over rain water
as far as the need to add micronutrients, potassium, or iron.

Use the Reverse Osmosis water or the lake water, just because it will be
easier to get your calcium levels up to where they ought to be by adding
calcium carbonate.  This is especially true for tanks that are not CO2
enhanced. The lake water is probably fine, except that you do have to worry
about adding unwanted hair algae or other organisms with the lake water.

Paul Krombholz in hot and dry (for this time of the year) central
Mississippi, where we need rain badly.