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I don't recall that anyone responded to this, so I thought I would.
Back on Friday, Christine M wrote:
> I have come to the conclusion that I need to supplement my tank with
> calcium. In particular, I am having a terrible time growing regular
> old swords. Nearly everthing else thrives.
A while back someone asked about what plants are good indicators for
different nutrient problems. As near as I can tell "regular old swords"
(E. amazonicus or E. bleheri) are a good indicator for low calcium. They
seem to show the symptoms before anything else.
> Currently I mix my water from RO with RO Right (or something like it),
> as well as Baking soda and Epsom salts (about 1.5 tsp of each per 30
> Since the goal is very soft water, I would rather not raise the GH
> much, and I think I need the Mg in the epsom salt, so I was hoping to
> replace the baking soda with calcium carbonate, which, if I understand
> the chemistry correctly, would allow me to raise the KH without
> raising the permanent hardness much.
Calcium carbonate raises both general hardness and alkalinity (KH). I'm
not sure what you are referring to as "permanent hardness". The general
hardness added by calcium carbonate is entirely temporary hardness, but
the difference between permanent and temporary hardness is trivial
unless you're going to boil the water.
Don't keep the water soft for the sake of your plants.
> Does anyone know of a source of calcium carbonate? Would, for
> example, one of the reef calcium supplements serve this purpose?
Limestone and/or dolomite chips sold in home centers and nurseries are a
source of calcium carbonate. Dolomite chips also provide magnesium.
Shells are also a source of calcium carbonate, and oyster shells are sold
as a dietary supplement for not much money. If you use a dietary
supplement, then read the label carefully. The supplements often come
with a lot of things, like binders, colors and flavoring that you may not
want. The cheapest brands might carry the fewest extras
Chips can be put into a filter, or dumped into the tank. Shells can be
placed in the tank, and the pills can be ground up and slowly dissolved.
It's probably easier to control the result by using the ground up pills.
Reef calcium supplements, aside from being remarkably expensive, aren't
necessarily calcium carbonate. They may be calcium hydroxide, calcium
chloride or solutions of either of those. But should you want to play
with some... I used a reef supplement a few weeks ago to give one of my
tanks a one-time-only shot of calcium. I wasn't concerned about
alkalinity. It worked just fine.