The key to healthy fish is healthy tank water. Here’s how to check your aquarium health and stop your fish looking green around the gills.

Neon tetras
The easiest way to check your fish tank water is to buy a good all-round tester kit. The key things to look out for are ammonia, nitrite, nitrate and pH. These compounds will be kept largely in check with a good mechanical, chemical and biological filter. But it’s a delicate balance, so check your tank’s water health regularly. Remember that you can always bring in a sample of 100mL of your aquarium water and have it tested for free at your local Petbarn.


The number one killer of fish is ammonia. It forms the first part of your tank’s nitrogen cycle and comes from fish waste and uneaten food. Whether your aquarium is fresh or salt water, you want the ammonia level to be 0.0ppm or undetectable. Any higher and the water could be toxic for your fish and needs to be treated with an ammonia removal product. To stay on top of your aquarium’s ammonia levels, install an ammonia alert sensor.


The second part of the nitrogen cycle is nitrites. They are the result of ammonia being broken down by the natural bacteria in your tank. Again, nitrites are toxic and should be in concentrations no greater than 0.0ppm. To contain toxic nitrite levels during a cycle, use a conditioner.


Nitrates come from the break down of nitrites. This compound is not particularly dangerous for fish, but if levels rise it can become toxic and stresses a tank’s inhabitants. For freshwater tanks, nitrate should register below 40ppm. Acceptable levels vary among saltwater ecosystems but are generally lower. An appropriate filter media and regular water changes will keep nitrate levels down.


Recommended pH levels vary depending on the type of fish you’re keeping. A pH ranging from 6.5 to 7.5 is generally safe for most freshwater fish, while saltwater fish thrive in more basic water (upwards of 8). A pH alert sensor will let you know when to add pH down or pH up.

General health

  • Appropriate tank temperature varies greatly between species, so do your research. Make sure your tank is not directly exposed to sunlight
  • Change 25 percent of tank water every week to help remove nitrites
  • Use a gravel vacuum to remove any leftover food or fish faeces

30-Day Fish Guarantee

At Petbarn, we’re confident that the fish that leave our stores are happy and healthy. However, in the event you experience a problem, we will happily guarantee your new fish purchase for 30 days, so long as your fish has been placed into a suitable environment. Simply bring us a sample of the water from your aquarium for analysis, plus a copy of your receipt. Please ensure that the water sample is at least 100mL and in a clean container. With your water sample, we will provide you with a water parameter test, including the pH range, ammonia, nitrate, nitrite and other parameters if needed. We will help you identify areas of concern to ensure you are ready for your next fish purchase.