The (Desired) Water Parameters in a Freshwater Aquarium

Everyone always told me that I should measure my water parameters in my aquarium so I could keep a close eye on them. If anything would be off I could correct them. But what are these right parameters? After researching, these are the values I found to be correct.

ParameterFreshwater Aquarium
Temperature22° – 28°C or 72 – 82°F
Ammonia0 ppm
Nitrite0 ppm
Nitrate< 50 ppm

General Hardness (GH)

4 – 12 GH

Carbonate Hardness (KH)

4 – 8 KH
pH6.5 – 7.5

So with these values in mind, every time you check your water parameters you know if they are right. Chances are that you do not exactly know what all the values are for. Also, if a value is off what can be the cause and how can you alter it? These are the things that I am glad to tell you in the rest of the page.


  • 22 – 28°C or 72 – 82°F
  • Needs to be stable
  • Can vary for different species (for example discus)

If you are keeping tropical fish, they need tropical water temperatures. In an aquarium the temperature is controlled by a heater, that keeps the water at the desired temperature. Your house is temperature controlled, so is an aquarium.

Stability is key, this goes for most water parameters and I am going to repeat this more often.

In general, a freshwater (community) tank’s temperature is set between 72 and 82 degrees Fahrenheit or 22 to 28 degrees Celsius. There are also different species that require a different temperature, the most popular example are discus fish.

Discus fish require a temperature between 24 – 30°C or 76 – 86°F, which is warmer than almost all other popular aquarium fish.

pH (Acidity and Alkalinity)

  • Stability is key, a fish can adapt to a pH that is slight off their preferred preference
  • Between 6.5 – 7.5 acceptable for most species

The lower the pH, the more acidic the water, while a higher pH raises the alkalinity of the water. The scale goes from 0 to 14, where 7 is neutral. Overall tap water has a pH of around 7.

Different fish have different pH preferences, but the most important thing is stability. Your pH needs to be stable. If the pH deviates a little from the fish’s ideal value, it can adapt to it. As long as it does not change rapidly, because these quick changes will kill all fish.

In general, a pH between 6.5 and 7.5 is good for a freshwater aquarium.

Something that I did not know before is that the scale of the pH is logarithmic. Meaning that if a pH drops from 7 to 6, the water is 10 times more acidic. If the water from from 7 to 5, the water is a hundred times more acidic.

How to Lower the pH

  • Filter over peat moss
  • Catappa leaves
  • Driftwood
  • Chemically

There are several things you can do to lower the pH, if this would be necessary for the fish you are keeping. You possibly have tap water that has a substantially higher pH than you want.

Because we already concluded that fish like a steady pH, and they do not like rapid changes, it would be best to change it gradually. This can be done using organic/natural ways to alter the pH.

Natural ways

The first organic way is to add peat moss to your filter. The peat moss will gradually change your water pH. There is not really a given dosage and time frame, just add it and measure regularly to see the effect.

Secondly, you can add catappa leaves to your aquarium. These also lower your pH. It is also claimed that they have a natural antibacterial effect on your tank, which makes them great to add to a tank with vulnerable fish fry. Catappa leaves are not that expensive, you can check the current price on Amazon by clicking this link.

The final organic way to lower the pH is by adding pieces of driftwood to the tank. Besides being an awesome way to decorate your tank, a great hiding place for your fish and also crucial for fish like (bristlenose) pleco’s, it also has an effect on the pH.

Important: All three ways mentioned above also stain your water. It will become yellow/brown-ish over time. Your fish will definitely not mind, and if you do you can reduce this by using active carbon in your filter.

Using chemicals

Besides natural ways to lower the Ph, there are also products available to achieve the same effect. A wide variety of brands offers products like “pH Lower” and “pH Down”.

You might want to use these products if you really struggle with the idea of stained water, or you think it is easier to use a chemical.
Although it is a possibility to use these, I would recommend against them. It is super easy add too much of the product, causing a sudden change in pH. This causes stress and is potentially even lethal for your fish.

How to Raise the pH

If you need to increase the pH to make the water more alkaline, you can use baking soda. Make sure you use baking soda with no other additives.

As a dosage, use 1 teaspoon per 5 gallons (18 liter). This will make sure the increase is a small and safe increment. Remember that your fish do not like a (rapidly) changing pH level.

If you want to be really sure that your fish do not experience any stress or even die, you can temporarily remove them and house them in another tank.

Make sure to measure the pH, and when it is at the desired level you can put your fish back in their original aquarium.

Ammonia, Nitrite and Nitrate

  • Both ammonia and nitrite should never be measurable when your aquarium is completely cycled
  • Some measurable nitrate is fine.

Moving on to ammonia, nitrite and nitrate. These nitrogen compounds are super important for your aquarium. They are rather easy to understand.

They are different stages in the nitrogen cycle. The first part is ammonia, which is converted into nitrite and finally into nitrate by beneficial bacteria that live in your filter.

To start off, what is the source of these substances? How do they come into the water of your aquarium?

Ammonia concentrations rise because of fish poop, uneaten food and rotting organic matter like plants. Ammonia is super toxic and should never be measurable in your aquarium. This translates into a desired ammonia concentration of 0 ppm.

The second stage is nitrite. Which is the product once the beneficial bacteria convert the ammonia. Although nitrite is less toxic compared to ammonia, it is still toxic at low concentrations. Nitrite concentrations should not be measurable in your tank water either. Keep your nitrites at 0 ppm.

The final stage is nitrate, do not confuse it with nitrite because they only differ one letter. When all ammonia is converted to nitrate, you are good to go. Nitrate is way less toxic, and if you keep your nitrate concentrations below 50 ppm there is nothing to worry about.

To remove nitrate, we as fish keepers do water changes. Another way is to use live plants to your advantage because they feed on nitrate. If you do not take care of your nitrate levels, they might raise until they pose a problem. Neglecting maintenance is often referred to as old tank syndrome. I wrote an informative article on it a while back.

GH (General Hardness)

  • Depending on fish that you keep
  • 4 – 12 GH is generally fine for tropical tanks
  • Cichlids need a higher GH, while discus need a lower GH

GH is an abbreviation for General Hardness, and is a measure for the amount of dissolved salts in your water. In particular, how much dissolved calcium and magnesium.

You are probably aware of the difference between soft and hard water, as this is also applicable for the tap water you have at home. With a low GH the water is soft, and with a high GH the water is hard.

If you want to monitor your GH values, you will need a test kit. The reason for this is that you can not just see a difference between soft and hard water.

But don’t worry! These test kits are not hard to use. And they are not expensive either. All you need is the GH and KH Test Kit from API, check Amazon for the current price.

You do not need to measure GH often, unless you have rather soft or rather hard tap water, and the fish that you are keeping prefer a GH somewhere in the middle.

KH (Carbonate Hardness)

  • Keep KH between 4 – 8
  • KH is a buffer for pH

KH is the abbreviation for Carbonate Hardness, where the K comes from the German word “karbonate”. It is a measure of bicarbonate (HCO3) and carbonate (CO32-) ions. These ions are a buffer that prevent the pH from dropping or changing.

If you have a low KH value, the pH of your tank water is more likely to crash. Therefore you should keep it above 4 dKH. (The d in dKH stands for degree, where one degree is equal to 17.9 mg/I or 17.9 ppm)

Another thing that you should know is that the nitrifying (beneficial) bacteria in your tank slowly consume the KH in your water. To balance this, your substrate generates more, you do water changes or you add the right chemicals.

Bart Sprenkels

I have been keeping multiple aquariums since I was 18 years old. Just like many of you, I started with two goldfish but quickly learned they were not suitable for aquariums. Later, I switched to a tropical community tank and I also have two pet musk-turtles in a bigger aquarium. You can read more about me here.

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