What is dH?

dH is a measure of the degree of General Hardness of water based on the amount of dissolved calcium carbonate present.  General hardness can also be measured in ppm (parts per million).

Most fish can survive in a wide range of water hardness, however dH can be particularly important in creating proper breeding conditions.  Water can be softened by filtering it through peat moss, boiling it or by passing it through a reverse osmosis filter.  Water can be hardened by subjecting it to crushed coral or dolomite.  Soft water needs more monitoring as the pH level becomes very unstable in soft water.

kH is another measure of water hardness.  It measures minerals other than calcium and magnesium and is not frequently used.