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How Long Will My Pet Fish Live? Depends on the tap water...

How Long Will My Pet Fish Live? Depends on the tap water...


Common Water-Related Reasons Your Fish Struggles to Survive

Have you ever brought home a brand new pet fish, only to have it turn belly-up as soon as you get it into its tank? Unfortunately, this is an all-too-common occurrence that may have you feeling green around the gills (so-to-speak). But there is hope! Tap water issues tend to be the culprit–so, we are stepping in to shed light on common fish tank problems (and ways to fix them).

Read on–it could be a life-saver!

Let’s Talk Tank Toxins…

Just as humans are negatively affected by toxins in their environment, fish are also impacted by contaminants in their surroundings. In fact, they are often more sensitive than humans. Toxic substances in water flow through fish gills–allowing toxins to enter their bloodstream directly. Fish may experience toxicity due to contaminated water to varying degrees depending on their:

  • Species
  • Size
  • Metabolic rate
  • While there are a slew of possible contaminants that could harm your fish, the following list of causes pose the most likely threats.

    Tap Score Water Testing

    Ammonia Toxicity

    Ammonia is a dissolved gas composed of nitrogen and hydrogen. Highly toxic to any fish, the only safe level ammonia to have in your fish tank is 0 parts per million (ppm). Concentrations of just 2 ppm can severely harm (or even kill) your fish. Ammonia poisoning may be attributed to:

  • An interruption that kills beneficial bacteria (due to power outage, filter exchange, etc.)
  • A change in the bio-load (i.e. if new fish are added the aquarium too quickly)
  • Signs and symptoms of ammonia poisoning in fish include:

  • Lethargy or hovering at the bottom of the thank
  • Red gills
  • Lack of appetite
  • In severe cases, external and internal bleeding before resulting in death
  • If you are concerned about ammonia toxicity in your fish, steps you can take include:

  • Conduct a partial water change in order to lower the pH to 7.0 or below. Toxic ammonia changes to harmless ammonium at this threshold.
  • Scoop out excess or unwanted organic matter floating in the tank
  • Reduce the feeding frequency. Uneaten food left floating can lead to increased ammonia concentrations
  • Aerate the tank via aeration pump. This will help diffuse the ammonia out of the water and into the air

  • Nitrite Contamination

    Like ammonia, nitrite is another dangerous chemical for aquariums that (ideally) should be kept at 0 ppm. Levels of 0.25 ppm or higher can cause irreparable damage. Nitrite is indirectly produced by the breakdown of fish waste, uneaten food, or decaying organic matter. The more fish in your tank, the higher the nitrite concentration will likely be. In order to ensure acceptable nitrite levels, it is crucial to not overfill your tank, as well as routinely clean out uneaten food or decaying matter.

    Nitrite enters into the fish’s bloodstream and binds to hemoglobin cells, which carry oxygen throughout the fish’s body. As a result, the fish’s blood is rendered unable to carry oxygen and essentially suffocates.

    Signs and symptoms of nitrite poisoning in fish include:

  • Gasping for breath at the water surface
  • Listlessness
  • Tan or brown gills
  • Unusually rapid gill movement
  • If your fish is exposed to nitrite for extended periods of time (even at low levels), their immune system, liver, and gills may all get damaged.

    If you are concerned about nitrite toxicity in your fish, steps you can take to remedy the problem include:

  • Conduct a partial water change
  • Add half an ounce of salt (preferably chlorine salt) per gallon of water
  • Reduce feeding
  • Increase aeration
  • Partial water changes, feeding reduction, and increased aeration are all ways to remove nitrite build up, whereas chlorine salt will help prevent methemoglobin build up in your fish’s body.

    Elevated Carbon Dioxide Concentrations

    Carbon dioxide levels above 25 to 30 parts per million can be dangerous for fish. When carbon dioxide concentrations get too high, the fish can suffocate. Causes for increased carbon dioxide in your fish tank can be attributed to:

  • Malfunction in the carbon dioxide reactor
  • Insufficient lighting that renders plants unable to absorb carbon dioxide
  • Signs and symptoms of carbon dioxide poisoning in fish include:

  • Rapid breathing
  • Gasping for air
  • Staggering swimming behavior
  • A long-lasting solution to elevated carbon dioxide concentrations in your fish tank is to heavily aerate the tank via surface agitation. Moving the surface water around will cause the carbon dioxide to dissipate.

    Heavy Metals Toxicity

    Heavy metals–like iron and copper–can be fast acting poisons in a fish tank. While they are crucial for life at low levels, they can be lethal and may not present any warning signs–so it is crucial to prevent heavy metal contamination from the get-go. Knowing the hardness of your water can help you determine how susceptible your fish are going to be to heavy metal toxicity. Some research has shown that the heavy metal toxicity in fish is lower in harder water than in softer water.


    Even slightly elevated iron concentrations, anywhere from 0.1 to 10 ppm, can be lethal. The pH of the water can also affect the rate at which iron impacts your fish. Iron hydroxides can form on fish gills if pH levels exceed 7.0–leading to:

  • Mucous secretion
  • Gill tissue swelling
  • Suffocation
  • Iron toxicity is further exacerbated by increased aeration. The best solution to elevated iron levels is to identify what concentration of iron your tap water has and pick a filtration technique that suits the level of iron (e.g. water softener, mechanical filtration, or a more advanced filtration device).


    Copper may be introduced into your water through your copper plumbing, but it is also a common treatment (in the form of copper sulfate) for fish parasites. Toxicity may occur at levels as low as 0.006 ppm (for long-term exposure) or 0.1 ppm (for short-term exposure). Yet some medicinal applications of copper maintain copper levels over 1 ppm during application. It all depends on the fish and the context, so it’s best to to consult a fish specialist before applying copper medicinally.

    The best way to remove heavy metals from your tank water is to use a water conditioner and heavy metal remover–which can detoxify the metals and protect your fish from chlorine and its byproducts. Chlorine and its byproducts are a bit topic at Tap Score, and they can also be harmful to your fish in excessive levels.

    What’s in my tap water?

    Ammonia, nitrite, CO2, and heavy metals are some of the most common reasons pet fish don’t survive at home, and we hopefully this guide will prevent future fish fatalities. However, if you are concerned about your tank, fish, or other aquatic life–it’s always a good idea to consult your local pet shop or aquarium store.

    If the solutions above aren’t working, try testing your tap water to see what might be hurting your fish.

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    About The Author


    Kate leads operational strategy as COO at Tap Score and SimpleLab. She oversees daily, as well as long-term logistics for tens of thousands of environmental samples across hundreds of certified laboratories. However, she started her environmental testing career by way of scientific blog writing at Tap Score and it continues to be one of her favorite aspects of the business. Outside of Tap Score, Kate loves making homemade pasta, floral arranging, and singing along to Dolly Parton tunes.
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