How much detergent should I use in my dishwasher?
The amount depends on your water hardness. For soft water (0-3 grains), use 1 tablespoon in the main cup and 1 tablespoon in the open cup for POTSCRUBBER and NORMAL WASH cycles. For hard water (7-12 grains), fill both cups completely full. For extremely hard water (12+ grains), a water softener is recommended.
From the official GE GSD820 Dishwasher manual, page 7
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