Water Chemistry in Aquariums: Why It Matters and What You Need to Know

What Should You Test in Aquarium Water?

Maintaining the right water parameters is essential for fish health. Regular testing helps detect imbalances before they become life-threatening. Below are the key water parameters every aquarist should monitor:

• Ammonia (NH₃/NH₄⁺): Highly toxic to fish. Even a small amount (as little as 1 PPM) can be fatal. Ammonia buildup often results from uneaten food, fish waste, and decaying plants.
• Nitrite (NO₂⁻): Less toxic than ammonia but still dangerous. Elevated nitrite levels can cause fish stress, damage gills, and lead to death if left unchecked.
• Nitrate (NO₃⁻): Less harmful than ammonia and nitrites, but excessive amounts can weaken fish immunity. Ideally, nitrate levels should be below 10 PPM. If they rise above 50 PPM, fish may become stressed and more susceptible to diseases.
• pH Level: Measures water acidity or alkalinity. While most fish can adapt to a range of pH levels, some species—such as African Cichlids—require a specific range for optimal health.
• General Hardness (GH): Indicates the amount of dissolved minerals, primarily calcium and magnesium, in the water. It affects fish osmoregulation and plant health.
• Carbonate Hardness (KH): Also known as buffering capacity, KH helps stabilize pH. Low KH can result in sudden pH fluctuations, which may be harmful to fish.

Regular water testing ensures a stable and healthy environment for your aquatic pets. Knowing these parameters allows you to make necessary adjustments and prevent potential issues before they escalate.

How to Test Aquarium Water: Best Methods Explained

Regular water testing is crucial for maintaining a stable and healthy aquatic environment. Different types of test kits are available, each with varying levels of accuracy and ease of use. Below are two of the most commonly used methods:

1. Test Strips

Pros: Quick, easy to use, and affordable.

Cons: Less accurate than liquid test kits.

Test strips provide a general overview of water conditions, measuring parameters like pH, GH (General Hardness), KH (Carbonate Hardness), nitrites, and nitrates. While they are useful for routine checks, they are not precise enough for diagnosing serious issues. Many aquarists use them for regular monitoring, especially in stable tanks.

2. Liquid Test Kits

Pros: Highly accurate, ideal for detecting specific toxins.

Cons: More expensive and requires more effort to use.

Liquid test kits provide more precise readings for ammonia, nitrites, nitrates, and pH. They are particularly useful during the aquarium cycling process and when troubleshooting water quality issues. Due to their cost, many aquarists use them selectively when needed.

Choosing the right test kit depends on your needs. If you have a well-established aquarium, test strips may suffice for routine checks. However, for new setups, breeding tanks, or troubleshooting, liquid test kits are recommended for accuracy.

When and How to Adjust Aquarium Water Parameters

Maintaining stable water chemistry is essential for a healthy aquarium. If certain parameters go beyond safe levels, they must be corrected promptly. Below are the key factors to monitor and how to adjust them effectively.

1. Ammonia: Immediate Action Required

Why it matters: Even small amounts of ammonia (as low as 1 PPM) can be lethal to fish.

How to fix it:

• Perform an immediate water change (25–50% depending on severity).
• Check for causes such as overfeeding, overstocking, or a clogged filter.
• Ensure your filtration system is functioning properly. Clean filters using old tank water to preserve beneficial bacteria.

2. Nitrites: Dangerous and Should Be Addressed Quickly

Why it matters: High nitrite levels reduce oxygen in fish blood, causing stress and suffocation.

How to fix it:

• Perform a water change and monitor daily.
• Ensure proper filtration and avoid overfeeding.
• Introduce live plants to help absorb excess nutrients.

3. Nitrates: Manage with Water Changes

Safe range: Ideally below 20 PPM, but up to 50 PPM can still be tolerated.

How to fix it:

• Perform regular water changes based on test results.
• If your tank is overstocked, increase water change frequency.
• Consider adding live plants to help lower nitrate levels naturally.

4. pH: Best Left Alone Unless Necessary

Why it matters: Fish can adapt to a stable pH, but sudden changes can be harmful.

How to fix it:

• Test your water source to know its natural pH.
• If adjustments are needed, use natural methods (e.g., driftwood to lower pH, crushed coral to raise pH).
• Monitor pH levels frequently when making changes.

5. GH & KH: Buffering and Hardness Adjustments

Why it matters: GH (General Hardness) and KH (Carbonate Hardness) affect pH stability.

How to fix it:

• Increase GH/KH using crushed coral, limestone, or commercial buffers.
• Decrease GH/KH using distilled water, rainwater, or peat moss.
• Frequent testing is recommended when making adjustments.

By maintaining proper water conditions and making gradual changes when needed, you can ensure a stable and healthy environment for your fish.

Water Chemistry FAQs: Common Questions & Expert Answers

To provide the most comprehensive resource on aquarium water chemistry, we have compiled real questions from our community along with expert answers. These FAQs cover essential topics, from ammonia levels to water hardness, helping you maintain a healthy aquatic environment.

If you have any questions, feel free to use the form at the bottom of this page to get expert advice!

• How do fish react to high ammonia levels in aquarium water?

  Fish exposed to elevated ammonia levels suffer from chemical burns, particularly in sensitive areas like their gills, gill plates, and eyes. Signs of ammonia poisoning include swollen or reddened gills and slightly cloudy eyes. In severe cases, ammonia burns can lead to suffocation as the gills become too damaged to function properly. Additionally, visible burns may appear on the fish's scales and fins.

  Aquariums, ponds, and natural ecosystems have a biological filtration process known as the nitrogen cycle, which helps regulate ammonia levels. Understanding and maintaining this cycle is essential before introducing fish to a new tank.

• When should I perform a water change while cycling my aquarium?

  During the aquarium cycling process, performing water changes too early can extend the cycle. It is generally recommended to wait until ammonia levels reach zero and nitrate levels decrease before conducting a water change. Initially, nitrates will be high, but once the cycle is complete, regular water changes will help maintain water quality and prepare the tank for fish introduction.

• What water parameters should I test in my aquarium?

  To ensure a healthy aquatic environment, test for the following key water parameters:

  • pH: Measures acidity or alkalinity.
  • Ammonia: Highly toxic to fish, should always be at 0 PPM.
  • Nitrites: Harmful at high levels, should be at 0 PPM.
  • Nitrates: Less toxic but should be kept below 20 PPM.
  • Water Hardness (GH & KH): Affects fish health and tank stability.
• Why is testing for ammonia in aquarium water important?

  Ammonia is extremely toxic to fish, causing chemical burns on their gills and scales. If ammonia levels rise too high, it can lead to suffocation and fish fatalities. Regular testing allows you to detect ammonia spikes early and take corrective action, such as water changes and improved filtration.

• How often should I change my aquarium water if my fish eat a lot?

  Frequent feeding leads to increased waste, which can raise nitrate levels. To maintain optimal water quality:

  • Test for nitrates regularly—if levels exceed 20 PPM, increase water changes.
  • For most tanks, changing 10% of the water weekly is sufficient.
  • For tanks with heavy waste-producing fish, increase water changes to 20% per week.
• Which tetras can tolerate hard water?

  Most tetras prefer soft, acidic water, but some species can adapt to harder conditions. Hardy tetra species that may survive in hard water include:

  • Lemon Tetras
  • Red-eye Tetras

  Keep in mind that true hard water starts at a pH of 7.7 and above, not at 7.0-7.5.

• Why is my aquarium water hard?

  Water hardness varies by region and depends on the mineral and carbon content in the local water supply. As water travels through rocks and soil, it absorbs minerals like calcium and magnesium, leading to increased hardness.

• Why do tropical regions have less standing water?

  In hot, humid tropical climates, water evaporates quickly due to high temperatures. This moisture forms clouds, which later release rain over cooler regions. This process is part of the natural water cycle.

• Why do some plastic aquarium ornaments glow underwater?

  Some decorations glow because of aquarium lighting reflection, while others are coated with luminescent paint designed to emit a glow in low light conditions.

• What are the ideal water conditions for Oscars?

  Oscars thrive in the following water parameters:

  • pH: 6.5 – 7.5
  • Temperature: 75 – 86°F (24 – 30°C)
• What are the water requirements for Mosquito Fish?

  Mosquito Fish prefer:

  • pH: 6.0 – 8.0
  • Temperature: 69 – 86°F (20 – 30°C)

  More details can be found here.

• What are the ideal water parameters for Tiger Barbs?

  Tiger Barbs require the following conditions:

  • pH: 6.5 – 7.5
  • Temperature: 68 – 77°F (20 – 25°C)
  • Water Hardness (dGH): 4 – 12
• What water conditions do Striped Catfish need?

  Striped Catfish prefer:

  • pH: 5.8 – 7.5
  • Temperature: 75 – 86°F (24 – 30°C)
  • Water Hardness (dGH): 4 – 18
• What are the ideal water conditions for Red Devil Cichlids?

  Red Devils require the following parameters:

  • pH: 6.0 – 7.5
  • Temperature: 71 – 82°F (22 – 28°C)
  • Water Hardness (dGH): 10 – 22
• What are the ideal water conditions for Puffer Fish?

  The water requirements for puffer fish vary by species. They can be classified into:

  • Freshwater species
  • Brackish water species
  • Saltwater species
  • Asian and African varieties

  For detailed care guides on specific species, check these links:

  • Malabar Pufferfish
  • Giant Puffer Fish
  • Red-spot Puffer
  • Mekong Puffer

  You can also search within aqua-fish.net for more information.

• What is the correct GH (General Hardness) for an aquarium?

  There is no universal GH level, as different fish species thrive in different water hardness levels.

  Recommendations:

  • Test the GH of your tap water to determine its baseline.
  • Choose fish that naturally adapt to your water hardness.
  • If needed, use an RO (reverse osmosis) unit to soften the water.
• How can I lower water hardness in my aquarium?

  If your water hardness (GH) is too high, try the following methods:

  • Partial Water Changes: Replace up to 50% of the tank water with softer water.
  • Regular Water Changes: Weekly changes (10-20%) help reduce mineral buildup.
  • RO Water: Mixing in reverse osmosis (RO) water gradually lowers hardness.
  • Driftwood & Peat Moss: These natural materials release tannins that soften water.

  With consistent maintenance, GH can drop from 28 to 10 within 4-6 weeks.