Tim's Tropical Fish - Saltwater

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dH - Saltwater Hardness

Water Quality

Hardness (GH)



Very soft




4 - 8

70 - 140

Medium Hard

8 - 12

140 - 200


12 - 20

200 - 350

Very Hard

20 or more

350 or more

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).

Medium Hard levels are recommended for most saltwater fish, but they can survive in a wide range of water hardness.  However dH can be particularly important in creating proper breeding conditions.  Water can be softened through a reverse osmosis filter.  It can be hardened with additives.  kH is another measure of water hardness.  It measures minerals other than calcium and magnesium and is not frequently used.