Hi all,
Can I just use tap (I have soft water if that makes a difference), or boiled but not cooled?
I should have said that you can use the warm water, and that most salts are more soluble in warmer water. The exception to the solubility rules are the carbonates, and that is because their solubility is dependent upon dissolved CO2, and all gases are less soluble at warmer temperatures.
When we boil the water all of the (bi)carbonate will come out of solution as "scale", if we pour off, and strain, the boiling water we have removed all the <"
temporary hardness"> (the carbonates), but you haven't changed the amount of calcium (Ca), it is still there as the dGH or "permanent hardness", the hardness that can't be removed by boiling.
If we let the water cool again, without straining out the "scale", the carbonates will just go back into solution as the water cools and atmospheric CO2 re-dissolves.
use straight tape water some people report precipitate forming in the macro solution due to the calcium in hard water forming insoluble calcium phosphate (or sulphate ?)
Yes it is a combination of calcium (Ca), pH and (bi)carbonate that cause the problems in harder water.
For calcium, nearly all compounds insoluble, or very sparingly soluble in water. Some compounds are soluble in weak acids (like CaCO3), calcium sulphate (CaSO4.2H2O) has a solubility of ~2g in one litre, and calcium phosphate (Ca3(PO4)2) a solubility of about 0.2g in one litre.
For the micro solution at pH values above pH 7 you also have "spare" OH- ions (that is how pH is defined), and they will form insoluble compounds like
<"iron hydroxides">, if you have carbonates you will also get insoluble <"
iron carbonates">.
RO (or rain) water doesn't have any dissolved ions, so none of these issues occur.
Soft water doesn't have any carbonates (or calcium in the UK), so you've avoided those issues.
However, in the UK even soft water now has a high pH, due to added NaOH, but there aren't actually many OH- ions (because NaOH is a "strong base"), a so a small addition of a weak acid (<"l
ike citric or acetic acid">) will neutralise the OH- ions.
Acids are "H+ ion donors" and bases are "H+ ion acceptors", in this case we only need to add as many H+ as there are OH- ions (to form H2O) and get back to the neutral pH7.
cheers Darrel