Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If you are keeping livestock that has been raised in captivity for many generations, and do not plan on breeding then let the water be, and quit worrying.
However, here is a more complex answer:
Fish are adapted to the mineral levels in the water, the pH is secondary.
Do some research about the livestock you want to keep. Find out their optimum GH, and if they come from a black water river. Optimum pH, & TDS if you can find it.
Run some tap water a jar.
Test GH, KH, TDS, pH right out of the tap, then repeat in 24 & 48 hours.
Adjust the GH to suit your livestock.
If the GH or KH is too hard for your fish blend your water with distilled until it is good.
I use Equilibrium to raise the GH. If you think your tap water has unbalanced levels of Ca and Mg, then use which ever you need until you end up with a ratio that is more or less 4:1 Ca:Mg. You can get calcium or magnesium separately, and fresh water calcium tests, but this is not usually needed.
Set the KH pretty close to the GH. I have used baking soda and potassium bicarbonate to raise the KH. They both work just fine. Some people do not want the extra sodium from the baking soda.
If you are keeping black water fish then add peat moss to the water. Circulate it for several hours or overnight.
Test GH, KH, pH and TDS.
Allow this to sit overnight or so, and see if it stays the same, then test a few days later.
Now you have a recipe for how to make water for a delicate or special species of fish. You will do this for every water change. Top off with reverse osmosis or distilled water.