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Frank I. Reiter <FIR at istar_ca> asks "So how hard *is* my water?"
Sometimes the simple answer is right there in front of you! ;-)
If you have RO water all you need to do is weigh the various compounds
you add to the water and you can easily compute the milligrams of X
per liter of water that you add. If you dose each chemical separately
such as calcium carbonate and magnesium sulphate (epsom salts), you
can precisely control the concentration of each ion species. Remember
not to add chemicals to the water you add to replace evaporation. Top
up, siphon off 10 gallons (or whatever), add 10 gallons and add 1 or 2
tsps of calcium carbonate. Remember that you also need to compute your
magnesium and potassium requirements as you do using PMDD. I tend to
dose that on an irregular basis so adding it during water changes
makes sense. I tend to develop potassium shortage symptoms.
OK my turn to ask some questions:
Question (1) what is a good concentration for magnesium and potassium
in mg/l in a planted aquarium? Assume it has to be enough to supply
nutrient needs for 2-4 weeks in a strongly lit tank full of slow
growing plants without causing any problems by overdosing potassium.
(obviously some fast growth plants could soak up grams of nutrients
each week but who wants to chuck a pound of Ceratopteris each week?)
Question (2) How many tsps of hydrated magnesium sulphate (epsom salt)
and potassium sulphate do I need for 10 gals of water? Ok I can figure
this out if I know the answer to (1) since I have a periodic table and
can weigh teaspoons. By the way don't forget to factor in the weight
of 6 H2O for each MgSO4.
I'm kind of assuming that all the nitrogen requirements are being met
by fish food and wastes or from decomposition of substrate organic
Question (3) Are some plants sensitive to excess concentrations of
Calcium, Magnesium or Potassium? I've read in the t.f.h. Windenov
Tropica Catalogue, Aquariums Plants, A Complete Introduction, that
many species of Crypts do not tolerate an excess of Calcium ions. How
much is too much?
Steve P in Vancouver