Fish need clean, chemically balanced water to thrive.
Your aquarium’s environment
An aquarium is a delicately balanced ecosystem that relies on “good” bacteria to keep fish healthy. When everything is working right, helpful bacteria grow in the aquarium’s gravel and filter. There, they help break down the ammonia and nitrite found in fish waste—which, if left unchecked, would be toxic to your fish.
When you first set up your aquarium, you’ll need to encourage the growth of these beneficial bacteria. The process, called cycling, can take 4 to 6 weeks. Using bacteria starters can reduce the cycling time to 1 to 3 weeks. Here’s how to start:
- Set up and fill the aquarium with water. Do not add fish. Run the aquarium filter for at least 24 hours.
- Introduce a small number of danios, gouramis or livebearers—hardy fish that aren’t as sensitive to ammonia or nitrites. (The number of fish will depend on the size of the aquarium; ask a PetSmart associate for advice.)
Over time, the beneficial bacteria should kick in and balance the chemistry in the aquarium. Once the water is ready, you can slowly introduce new fish.
How do I care for aquarium water?
- Be sure to check the water temperature in your tank every day.
- Replace 10% of the tank with clean water
- Test the water's pH, ammonia, nitrite, nitrate, hardness, alkalinity and chlorine
- Clean away any algae
- Vacuum aquarium gravel
- Replace 25% of the tank with clean water
- Inspect filter; rinse or replace the cartridge, carbon and pre-filter if necessary
- Clean away any algae
- Remove and clean plastic plants and decorative items
- Replace air stone
- Prune live plants if necessary
What chemicals are in aquarium water?
- Normal pH range: 6.5 to 8.2
- This is the acid/base activity in the water
- Rapid changes in pH levels are unhealthy for your fish
- The stability of the pH is related to water alkalinity.
Chlorine and Chloramine
- Normal results: 0.0 mg/L
- Chlorine and chloramine are found in city water and must be removed for fish.
- The chlorine in tap water is toxic to fish. Use a dechlorinator to clean any water before adding it to the aquarium.
- Normal results: 0.0 to 0.25 mg/L
- Once an aquarium has been cycled, it should have no ammonia. In new aquariums, ammonia neutralizers can be used to lower ammonia levels.
- Normal results: 0.0 to 0.5 mg/L
- Nitrite reduces the oxygen in your fish’s blood. If nitrite levels spike, change the water until it is at a safe level. You can also add aquarium salt to your tank (use 1 to 3 teaspoons per gallon, 0.1-.03%) to reduce nitrite toxicity.
- Normal range: 0 to 40 mg/L
- Nitrate encourages algae, so keep the levels low. A water change will help lower nitrate levels.
- Normal range: 100 to 250 mg/L
- Hardness refers to the levels of calcium and magnesium in the water. Test the hardness of your tap water and make changes to the aquarium water as needed.
Water with high hardness usually has a high pH. Softening the water will lower the pH level.
- Normal range: 120 to 300 mg/L
Low alkalinity can result in a sudden change in the tank’s pH level that may be deadly to your fish. Test tap water alkalinity and change water as needed to maintain proper alkalinity.
- Increase the alkalinity of the water to stabilize the pH level.
- Normal range: 74 to 82 degrees Fahrenheit. (23 to 28 C)
- Sudden swings in temperature can harm fish. Use an aquarium heater to keep a consistent temperature.
Shop water test kits Shop water conditioners
What kind of filtration does my aquarium need?
There are 3 methods of aquarium filtration: biological, mechanical and chemical. Your aquarium needs all 3 types to neutralize ammonia and nitrites and remove debris and contaminants. These common filtration systems employ all 3 methods:
- Under-gravel filter: A slotted plate beneath the gravel bed circulates water continuously.
- Power filter: Ideal for tanks up to 55 gallons, a power filter can be combined with an under-gravel filter for aquariums with a lot of fish.
- External power filter: Located on the back of the aquarium, this style draws water from the tank and pumps it through a replaceable cartridge.
- Canister filter: Ideal for aquariums 55 gallons and larger.