20 Chapter 1 Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery. 39Copyright (c) 2005 John Wiley & Sons, Inc.Chapter 1 Introduction to Statistical Quality Control, 5th Edition by Douglas C. Montgomery. 40Copyright (c) 2005 John Wiley & Sons, Inc.
Water hardness is a measure of the dissolved mineral content of water. There are two types: the general hardness (GH) and carbonate hardness (KH). When keeping freshwater fish and plants, the GH and the KH of aquarium water should match their natural habitat.
Absorbed dose is measured in joules/kilogram, and a quantity of 1 joule/kilogram has the special unit of gray (Gy) in the International System of quantities and units. (In terms of the older system of radiation quantities and units previously used, 1 Gy equals 100 rad, or 1mGy equals 0.1 rad.)