Rule 10


Hardness and pH, What Do I Really Need to Know?

Before adding chemicals to your water, test your tap water. Use any inexpensive water test kit to make your calculations. Write your findings in a log book (I like to use an inexpensive folder or composition book) and keep it with the other aquarium supplies.

Make it a habit in your first year of fish keeping to do a water test on your tank before doing the monthly maintenance on the tank. 

This simple task will give you a visual guide to how quickly water in the tank will change in just four weeks.

What is Potential Hydrogen (pH)? pH is the measure of free hydrogen in the water. Don’t worry you do not have to remember this bit. I like to know the meanings of acronyms as it helps me remember their meanings.

Why is pH important? pH is important because it measures water solubility. For instance, water with an alkaline pH of 8.0 has less solubility than water with an acidic pH of 6.0. Meaning that if your aquarium water has a pH of 6.0 other elements (metals/gases) that come into contact with the water will leach into the water more rapidly and easily than if the water had a pH of 7.0 or 8.0. This leaching of elements could be dangerous to your fish. Hence the reason for watching the pH values of your tank.

The pH Scale

We measure pH on a scale of 0.0 (acidic) – 14.0 (alkaline/ basic) pH. For our purposes we want our pH to be as close to neutral (7.0 pH) as we can get. When you are more experienced you can begin playing around with pH levels for certain species of fish.

How To Adjust the pH to the Neutral Zone 

When I began keeping fish in the early 1970’s I used the chemicals sodium bicarbonate to make water more alkaline and sodium bi-sulfate to make water more acidic. Today we can purchase pre-mixed and pre-measured chemicals ready for use in your tank. This is as easy and mistake proof as you can get when dealing with pH values in the home aquarium. Remember, when adding any chemical please test your water between doses.

Sodium Bicarbonate

Sodium Bisulfate

pH scales

pH What does the pH represent

US Gov Alkalinity

Hard Water or Soft Water

Hard water has trace elements and minerals like calcium, potassium, magnesium, manganese, potash and iron in the water. These dissolved minerals make the water hard. The more minerals in the water the harder the water. Less minerals in the water, the water will be less hard.

Water that is completely demineralized through steam distillation is soft and has a hardness of 0.0.

Many of the Amazon Basin fish like somewhat soft water. Goldfish, live bearing fish, African Cichlids and salt water fish like their water hard.

Hard Water Map and Scale

Water Softeners

Most water softeners will remove minerals using salt making the water soft. The process also adds salt to your water. The amount of salt added to the water is usually not enough to harm your fish. If your fish need hard water you will need to add trace minerals back into the water. Live bearing fish and goldfish will need trace minerals to replace minerals used in bearing young and rapid growth rates.

City Water or Well Water

If you have city water you need to add a chemical to remove the chlorine and ammonia compound added to the water. Well water does not have any chlorine added to it so you will not need to treat the water for chlorine.


More about hard water


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