In this blog I provide guidance on improving your soft tap water by adding essential minerals and, importantly, how to avoid the steady increase in these minerals due to evaporation and other contributing factors over time. I also help you understand your aquarium's GH and KH, going beyond basic water change advice.

General Hardness (GH) and Carbonate Hardness (KH): Are you testing for them in your planted aquarium? If not, you might be overlooking two of the most important yet often least understood water parameters. The Practical Aquarist is dedicated to bringing GH and KH into the spotlight and providing clear guidance on understanding, testing, and maintaining these essential elements for a thriving planted tank.

6 degrees of German hardness (6 °dH) sits right in the sweet spot for many common freshwater community fish, which do well between 4 °dH and 8 °dH – and represents my target for optimal planted aquarium water. In these pages, I focus specifically on using soft tap water, recognizing that tap water rarely provides truly ideal conditions for a thriving aquarium right out of the faucet.

Personal Anecdote: The Importance of Routine GH and KH Testing

My planted aquarium recently revealed a GH reading of 14 °dH and a KH of 7 °dH—significantly higher than the ideal range for my tetras and shrimp. This discovery, which followed a period of complacency in my GH/KH testing routine, prompted me to deepen my understanding of GH/KH management and ultimately led to the insights shared in this article series.


It also changed my personal practices. I now test GH/KH before every water change, remineralize my soft tap water only when needed, and utilize a nuanced water change strategy as described in Article #4.


Thank you, and I hope you find this blog interesting and helpful.


The Practical Aquarist



Location: Canada

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Optimizing Water Changes: How to Manage GH/KH for a Stable Aquarium

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Maintaining stable General Hardness (GH) and Carbonate Hardness (KH) is important for a thriving aquarium. Regular water changes are the primary tool for managing mineral accumulation and maintaining balance, but the type of water used for those changes plays a key role. This article focuses on optimizing water changes using soft water or water that closely matches your aquarium's current parameters. We assume you are already familiar with the concepts of soft and hard water. For reference, soft water is generally considered to have a GH of less than 4 °dH. Addressing Higher Than Desired Hardness with Gradual Reduction Should testing reveal general hardness (GH) and carbonate hardness (KH) levels exceeding your target, especially if regular testing has been absent, water changes with softer water offer a suitable method for gradual adjustment. While higher hardness may not present an immediate issue for all species, achieving the intended parameters often remains the goal. Importan...
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Understanding Water Hardness: GH vs. KH & Choosing the Best Water for Your Aquarium

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In this article, we will consider water. From pure water to soft and hard tap water, water hardness, and adding minerals to water. General Hardness (GH): The Mineral Content What most people refer to as "water hardness" is actually General Hardness (GH). GH measures the concentration of dissolved calcium and magnesium ions in water. These minerals are the primary contributors to what we perceive as "hard" or "soft" water. Higher concentrations of calcium and magnesium mean harder water, while lower concentrations indicate softer water. GH is typically measured in degrees of German hardness (°dH). Carbonate Hardness (KH): Buffering pH In contrast to GH, Carbonate Hardness (KH) measures the concentration of carbonate and bicarbonate ions in water. While KH is sometimes called "carbonate hardness," this can be misleading. KH does not directly contribute to the "hardness" in the way GH does (i.e., it doesn't make the water feel harde...
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