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Bacterial bloom in the aquarium: What you can do if the water becomes milky
Imagine looking into your aquarium – and instead of a clear view of your fish, all you see is cloudy, milky water. Everything seems blurred, almost as if shrouded in mist. Don’t worry, you’re not alone. What you are observing is most likely a so-called bacterial bloom in the aquarium – a phenomenon that many aquarists experience at some point. In this blog article, you can find out what exactly is behind it, why it happens and what you can do about it.
Bacterial bloom in the aquarium: What is a bacterial bloom?
A bacterial bloom in the aquarium is basically nothing more than a massive multiplication of bacteria in the open water. These are usually harmless, so-called heterotrophic bacteria that multiply explosively when the conditions are ideal. The result: your aquarium water becomes cloudy and milky – sometimes almost whitish – within a short time.
This cloudiness is caused by the high number of microorganisms floating in the water and refracting the light. Although it can look frightening, in most cases a bacterial bloom is not dangerous, neither for you nor for your fish – at least if it doesn’t last too long.
Bacterial bloom in the aquarium: Why does a bacterial bloom occur?
The causes of a bacterial bloom in the aquarium are usually a combination of several factors. It often occurs in newly set up aquariums – the so-called aquarium restart. In this phase, the biological balance in the tank is still very sensitive. There are hardly any established filter bacteria, the nitrogen cycle is still unstable and nutrients are available in abundance – perfect conditions for free-floating bacteria to multiply explosively.
However, a bacterial bloom can also occur in established aquaria. Perhaps you have recently cleaned the filter, reorganised the tank or added large amounts of food. All these changes can disturb the balance in the water. Organic waste in particular – such as leftover food, dead plant parts or too many nutrients – are the breeding ground on which bacteria quickly spread.
What happens in the aquarium during a bacterial bloom?
During the bloom, the bacteria consume oxygen and compete with other organisms – especially with your fish. This means that the oxygen content in the water can drop, especially at night. Your fish may then gasp for air at the surface or behave restlessly. Particularly sensitive species can become stressed.
The biological balance is also disturbed. Filter bacteria, which are responsible for breaking down ammonium and nitrite, may be inhibited in their work. This can lead to an increase in toxic substances such as ammonia or nitrite – both of which pose serious risks to your aquarium inhabitants.
How can you recognise a bacterial bloom?
Turbidity of the water is the most obvious sign. It is important to correctly identify the cause: Bacterial turbidity is usually milky white, while green turbidity is more likely to indicate an algae bloom. The latter is caused by too much light and nutrients, but is a completely different issue.
The time of occurrence also provides clues:
A bacterial bloom a few days after setting up an aquarium is almost normal.
However, if it occurs later or suddenly, you should check for possible changes or care errors.
What can you do if your aquarium is affected?
First of all, keep calm! In most cases, a bacterial bloom regulates itself as soon as the biological balance in the aquarium is restored. Nevertheless, you should remain vigilant and take a few measures:
Be careful not to feed too much. Anything that is not eaten serves as food for bacteria. Remove leftover food and organic material from the tank regularly. Careful partial water changes can also help – however, you should not do this too often, as this in turn can affect the beneficial bacteria in the filter.
It is also important that you do not over-clean the filter. A common mistake is to rinse out the filter thoroughly at the first sign of cloudiness – but this results in the loss of valuable bacteria, which are particularly needed at this time. Only ever wash filter media in stagnant aquarium water and never under tap water.
An additional supply of oxygen – such as an aerator – can make life easier for your fish during the bloom. In the case of heavy bacterial blooms and persistent problems, a UV clarifier can also help to reduce germs in the water. However, its use should be carefully considered and should not be seen as a permanent solution.
How can you avoid bacterial blooms in the long term?
In the long term, a stable, balanced ecosystem is the best protection. You can achieve this through regular but not excessive care, moderate feeding, a well-established filter system and sufficiently planted tanks. Plants not only help with oxygen production, but also compete with bacteria for nutrients.
Patience also plays a role. Especially in the initial phase of an aquarium, it takes time for a stable biological balance to be established. Give your aquarium this time and keep a close eye on how it develops.
Bacterial blooms in the aquarium – Conclusion
A bacterial bloom in the aquarium is not a reason to panic, but rather a sign that the balance has been disturbed. With a little background knowledge, a watchful eye and the right measures, you can usually get the problem under control. And the better you understand your tank, the easier it will be to prevent such phenomena – for permanently clear water and healthy aquarium inhabitants.
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