2Hr Aquarist Commentary: I use Sera's GH test kit to test for GH levels. This kit gives much clearer colors compared to API's kit. GH measures Calcium and magnesium levels (Combined) in a tank. Most plants do not require large amounts of either and tap water generally contains enough calcium that it need not be dosed. 2 to 3 dGH are good levels for most tanks and usually indicates that the water is quite soft. Shrimp/snail keepers might want to bump it up more depending on the species they are keeping. In hard water, GH may test upwards of 20 dGH. Generally, but not always, tap water that is high in GH tends to have higher KH as well, and this makes it unsuitable for growing plants that require softwater.
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