Causes and Signs of Low Oxygen in an Aquarium

When you think of a fish gasping for air, chances are that you only think of it happening above sea level, and at the end of a fisherman’s hook – not while they are swimming around happily in your aquarium.

Even so, low oxygen levels are renowned for being terrible silent killers of aquarium fish. And as most aquarium owners will agree, the last thing you want is to have to figure out saving your dying fish following a terrible incident.

One of the most important things to keep in mind when it comes to recognising the warning signs of your aquarium being low on oxygen is the fact that it is most often not visible from within the aquarium itself.

An immediate sign that can be picked up on is if you notice the presence of a clogged up, blocked filter. While a blocked air filter is an eyesore and can lead to an unpleasant, disgusting aquarium, at least it is an immediate giveaway. The clogged up appearance shows straight away that there’s a problem which needs fixing.

By contrast, there are only a few other immediate signs that even longtime fish owners might overlook. This makes it hard to recognise the warning signs of low oxygen in an aquarium fish tank.

Causes and Signs of Low Oxygen in an Aquarium, Aquarium Fish Tanks UK

Causes of Low Oxygen in Aquariums

What leads to low oxygen in fish tanks and what causes this problem? The easiest way to counter issues of low oxygen levels in fish tanks is to try and ensure it doesn’t become a problem in the first place. Knowing the most common causes of the issue can help you do just that.

Some of the most common causes of low oxygen in tanks include:

  • Overcrowding: The logic behind this is as simple as it is sad – if you overpack your aquarium with too many fish for its size, there simply won’t be enough food and oxygen to go around. It’s a horrible way to go, and not the fate you’d choose for your fishy friends. You might want to take fish tank recommendations as to size and capacity very seriously, and not overload your aquarium, helping your fish avoid suffering the consequences of your actions.
  • Warm Water: While different types of fish tanks and fish require different water temperature and climate, it is important to note that warmer water cannot store as much oxygen as cooler temperatures can.
  • Stagnant Water: Chances are you don’t want stagnant water anyway, as it’s a good indication you may have a filtration problem. Even if that’s not the case, however, stagnant water is undesirable as it typically contains less oxygen than water which is properly cycled.
  • Fish Waste: This is obviously another thing you shouldn’t want in your tank anyway, but if you needed even more incentive to clean your tank regularly, remember that excess waste and algae in a tank can dissolve oxygen in the water.

Identifying Low Oxygen

Your best bet is to watch for the kind of abnormal behaviour fish typically exhibit when they’re trapped in a low oxygen environment.

The immediate obvious things to look out for is fish spending an abnormal amount of time at the top of the tank, coming above the surface, and gasping for air once there.

With that said, even this can’t be the sole thing you look out for as some fish, such as labyrinth fish, usually stay close to the top of aquariums coming up for air. Again, the key thing to look out for here is behaviour abnormality. If your labyrinth fish or similar fish are up near the water surface, then that’s one thing, but if you have goldfish doing that, you may have a problem.

Treating the Issue

So, what can be done about low oxygen levels in your fish tank? Making sure it is not overcrowded is a good start.

You’ll also want to make sure to clean the tank regularly. The key thing here is to use a really good aquarium cleaner. One that has powerful cleaning ability and suction that can extract the harmful pollutants the lead to low oxygen levels.

Ensure that your aquarium filter is working properly and can continue to keep the tank clean around the clock. If there is a buildup of stagnant water or fish waste, clean the tank. Or get a better Aquarium filter.

With these simple steps, you can save your fish from suffering from low oxygen levels in their tank.

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