Aquarium Water Parameters

If you have ever tried to go on a fish forum to ask why your little fishy friend isn’t doing so well, you’ve probably been asked, “What are your parameters?” If you don’t know how to answer this, you are in the right place! Below I will try to explain the basic water parameters you should be aware of when keeping a freshwater aquarium. There are more specific parameters one can test for, but usually you will not need to unless you know you need to (know what I mean?).


The first and, for most of us, easiest to measure is temperature. Most fish in the hobby are tropical fish, and can tolerate similar ranges of temperature. The typical range in temperature for a tropical community tank (meaning a mix of different kinds of fish) is roughly 68F to 78F (20C to 25.5C). Each species is different, so you will need to research the ideal temperature range for that particular fish. Some species like Discus prefer their water above 80F, while Goldfish can be comfortable in water as low as 60F.

The takeaway from this segment is this: keep it consistent. In the wild, fish don’t generally experience big shifts in water temperature within short periods of time. Yes, over the course of the year water temperature changes with the seasons, but that is a very gradual process. In an aquarium, temperature shifts can be fast and dramatic, but they shouldn’t be. Something as simple as a light going on and off can raise and lower the water temperature. It’s good to keep a programmable heater in your tank to maintain a steady temperature. A sudden change of two degrees or more can cause stress to your fish. Continued stress can easily lead to illness or death.

Ammonia, Nitrite, Nitrate

This is a big one. Many a sickly fish can be attributed to poor maintenance of these three substances. Ammonia is highly toxic to fish and invertebrates. It comes mainly from fish waste and uneaten food. Nitrite, which is produced by Nitrosomonas bacteria is less toxic, but still no good to have in your aquarium. Nitrate, produced by Nitrobacter bacteria, is the least toxic of the three, but you should keep levels under control.

Ideally, in a planted aquarium with fish you would want 0ppm of both Ammonia and Nitrites. Since plants consume Nitrate, it’s good to have some in the water. In my opinion between 20ppm and 40ppm in a well-planted tank is ideal. For more information about how Ammonia, Nitrite, and Nitrate flow in an aquarium, please read my page on The Nitrogen Cycle. You may also want to read my page about Aquarium Filtration.

General Hardness (GH)

In regard to hardness, water can be described as either “soft” or “hard.” Soft water is that which has low concentrations of dissolved minerals and salts. Hard water has higher concentrations of those same minerals and salts. In the aquarium hobby, this usually refers to the levels of Calcium and Magnesium containing compounds in the water. Different species have different ballpark requirements for water hardness. Some plants prefer soft water, because the Calcium in hard water tends to bind to metals and other trace elements that plants need. Invertebrate species, like snails and shrimp, tend to prefer harder water because it has plenty of Calcium, which they need to produce healthy shells and exoskeletons. Again, all species have their own preferences, so you should research the specific needs of each.

Naturally occurring hard water often has more nutrients, because it usually comes up through the ground by way of springs. Rainwater is typically soft water,  because it is mostly falling through air. Some regions have “cleaner” rainwater than others due to varying levels of pollution and dust in the air.

Water hardness has a loose relationship with pH (acidity and alkalinity) because hard water can contain compounds that tend to raise pH. It is possible to have hard water with low pH.

pH (Acidity / Alkalinity)

pH is the measure of a solution’s acidity vs alkalinity. Acidic water has more positively charged hydrogen ions (H+) than it does negatively charged hydroxyl ions (OH-). Alkaline water is the opposite. Water is neutral when these two ions are of even concentration. The pH scale is a measure from 1 to 14. A pH value of 7 is neutral. Anything less than 7 (1 to 6.9) is acidic. Anything more than 7 (7.1 to 14) is alkaline (or “basic”). Fish tend to live between the pH values of 5 and 9, while most freshwater fish live happily within a range of 6.2 to 7.8.

Sudden or dramatic changes in pH can be deadly to fish and invertebrates. It is important to keep your pH consistent with only small, gradual changes when necessary.

Buffering Capacity (KH)

Buffering Capacity (aka Carbonate Hardness) is the measure of carbonate and similar substances in the water, and is tightly related with pH. It determines the relative ease with which pH can change within a body of water. The higher the KH of a body of water, the less dramatically the pH can change over a period of time. This is because carbonates will bind with excess Hydrogen ions (H+), preventing the water from becoming too acidic. So in essence KH is more practically described as a measure of how well an aquarium can resist drop in pH.

This is particularly important in planted aquariums. During the day, submerged plants consume Carbon Dioxide (CO2) in the water. Dissolved CO2 can form carbonic acid, and thus lowers pH in water. As the plants perform photosynthesis they consume the CO2 before it becomes carbonic acid, and pH gradually rises. At night when there is no light, the plants cannot perform photosynthesis. During this time, biological processes like cellular respiration in bacteria, fish respiration, and plant respiration produces CO2. As the level of CO2 rises, pH drops. If the drop is very deep this can cause stress in fish. In an aquarium with high KH, the excess ions bind to carbonate, and the pH remains stable.

Aquariums with a lot of biological matter: driftwood, fish mulm, and plant debris, will reduce the water’s pH over time. If left unchecked with water changes and/or addition of pH buffering compounds, this acidification of the tank water in conjunction with high levels of Ammonia and Nitrates can result in what is called “Old Tank Syndrome”, a very unhealthy environment for most fish and invertebrates.

Testing Water Parameters

There are many commercially available test kits out there. Some are specialized for measuring specific parameters, while others test for more than one. I would recommend getting two kinds of wide-spectrum test kits. First, the easy-to-use test strip kit. I like to use the Tetra EasyStrips 6-in-1. It is a very simple kit to use, and it measures: Nitrate, Nitrite, GH, Chlorine, KH, and pH. The downside is that it doesn’t measure Ammonia.

There is some controversy about test strips. Some say they can be inaccurate. So far they have worked well for me, but if you would like a more precise measuring kit, try the API Master Freshwater Test Kit. This is a liquid test kit. It’s not as easy as the strips, and requires some use of test tubes (glaven!). It’s still an easy kit to use and can be more accurate. It measures: Ammonia, Nitrite, Nitrate, and pH (both standard range and high range). The downside is that it doesn’t measure GH or KH.

Between these two tests you should be able to work out all of your tank’s basic parameters. It is a good idea to check daily when first setting up a tank and then weekly after it is settled in. As a tank stabilizes you can do less frequent tests, but it is good to do them regularly to keep on top of any problems before they become serious.

Now when someone asks, “What are your parameters?” you know exactly how to answer!

Let me know what you think of this article. Was it helpful?

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