The Salty Side: Saltwater Aquariums for Beginners

Why is my Saltwater Tank Cloudy Suddenly?

A cloudy saltwater tank is a common occurrence in new setups, where the water turns milky or opaque. This makes it difficult to see the fish, or anything in your tank, and can leave a new aquarist concerned for the wellbeing of their new inhabitants. It can also happen overnight in a well-established tank. In this article, we look at what makes a saltwater tank cloudy, and if you need to be concerned.

why is my salter tank cloudy?
Photo by B. Altieri

How do I clear up a cloudy saltwater tank?

Let’s be specific. There are a number of reasons that a saltwater tank might be cloudy, all of which are innocuous and nothing to worry about. Is cloudy water bad for fish? The simple answer is no. Below is a breakdown of the common causes that can turn a saltwater tank cloudy, with this article specifically addressing bacterial blooms.

  • Sand and flow: When setting up a saltwater tank it is not uncommon for new sand, either dry or live, to release ‘dust’ into the water column. Given time, these dust particles will settle, most often within a day or so. The sand may also be kicked up by your wave makers. This is a good opportunity to monitor the flow pattern and place the wave makers in the most suitable locations in the tank.

  • Snails: When adding snails such as Trocus snails to your tank, they act as an amazing clean-up crew, but you will not be the first reef keeper to find your tank entirely milky one morning. Snails release sperm and eggs at the same time to correspond with each other, and to have the highest success rate of new snail life. Although it may be shocking the first time you see it, your corals will love it, and in a matter of hours, your skimmer and filtration will clear the tank up.

  • Urchins: Like snails, urchins also release their gametes into the tank. The only difference is that we tend to keep more snails than we do urchins, so urchin sperm release can be less noticeable than snails’.

  • Skimmer: When you add a skimmer to a new tank, or even a seasoned tank, it can take them a while to settle down and produce skimate. In new tanks, the viscosity of the water is not ideal for a skimmer due to the lack of organics. With limited viscosity, the skimmer can produce too many micro-bubbles that will find their way into your display. Although this can be annoying, it causes no harm to your inhabitants. It will improve as your water becomes ‘older’ and more viscous.

  • Algae Bloom: An algae bloom is identifiable in a saltwater system by its cloudy green hue. Algae blooms are associated with the ideal conditions of high levels of light, lower pH (caused by increased carbon dioxide) and excessive phosphates in a saltwater tank.

  • Bacterial Bloom: A bacterial bloom is caused by excessive heterotrophic bacteria, and is the purpose of this article. Read on to discover how bacteria make a saltwater tank cloudy and what to do about it.

What causes a bacterial bloom?

A bacterial bloom can occur in a matter of hours, under the right circumstances. The heterotrophic bacteria responsible for bacterial blooms cannot synthesize its own food like nitrifying and denitrying bacteria (good bacteria responsible for converting ammonia into nitrate). It is completely dependent on complex organic substances for its nutrition. These bacteria break down uneaten fish food, fish waste and dead plant matter like nori, converting it into ammonia. They also reproduce far quicker than nitrifying bacteria, in as little as 15-20 mins. This is much faster than the reproduction rate of ‘good’ bacteria that can take up to 24 hours.

In a new setup, when the aquarist is reliant on nitrifying and denitrifying bacteria establishing the nitrogen cycle, however the bacteria responsible for bacterial blooms is reproducing at a much faster rate. It is utilising the organic waste in the sand and the potential die off from live rock.

In an established aquarium, the heterotrophic bacteria will utilise organic waste mainly in the sand, and if the waste is excessive, they can multiply rapidly causing a bloom.

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What does a bacterial bloom look like?

Depending on the level of waste available to the heterotrophic bacteria, your tank water can turn overnight. It could be slightly opaque, where you can still see the occupants in your tank, or it could be a complete white-out. The water may look like heavily diluted milk. In either case, you end up wondering what made your saltwater tank cloudy.

How long does a saltwater tank stay cloudy?

In new tanks, once the heterotrophic bacteria have bloomed, they would have done so using the limited organic waste available in the substrate. Once the available waste has been converted, the bloom will diminish and disappear. Typically, this could take a number of days in which you could sit it out. However, if you are already feeding fish, there is a possibility you are contributing the problem, and the increased longevity of the bloom.

You may be asking yourself, ‘Why won’t my cloudy tank go away?’. Simply put, the heterotrophic bacteria bloom will last as long as there is organic waste available to convert. For this reason, reefers often turn to UV sterilizers.

Why is my tank cloudy after I just cleaned it?

The scenario is, you have crystal clear water and you are being diligent in carrying out a water change. Boom! Inadvertently, you have made your saltwater tank cloudy. The reason this happens is there may already be a lot of organic matter and heterotrophic bacteria in your tank, but something was holding them back. With the water change, you have replenished trace elements that may have been depleted. With that crucial element reintroduced, it can trigger the bacterial bloom.

Will a cloudy tank fix itself?

As discussed above, the bacteria responsible for the bloom are reliant on organic waste. In a new set up, that organic waste is limited and the bloom should end in a matter of days. However, if you are already feeding fish, you may be contributing to the waste.

In a well-established tank, we cannot rely on the limitation of organic waste. If you experience a bacterial bloom in an established tank, then your organic waste has become excessive. Below are a few immediate actions you can take to mitigate any further blooms.

  • Ensure you are cleaning out your filter sock/cups out regularly to limit organic waste build up.

  • Do not over-feed. Any uneaten food will find its way into the substrate, contributing to the increased probability of another bacterial bloom, as well as future algae problems.

  • Siphon your substrate on your next water change. This will remove the majority of organic waste available in your saltwater tank.

Can too much light cause cloudy water in a reef tank?

The heterotrophic bacteria responsible for bacterial blooms are solely reliant on the availability of organic waste. Without the presence of organic waste, the bacteria diminishes. Light plays no part in their ability to reproduce, nor will it limit the intensity of the bloom if you turn the lights off. In short, too much light does not make a saltwater tank cloudy.

Unless, of course, you are not experiencing a bacterial bloom. You may be experiencing an algae bloom that presents as a greenish haze in your tank. Too much light can help the algae bloom proliferate.

Does cloudy water mean ammonia?

The bacteria responsible for your cloudy tank produce ammonia as a by-product of breaking down organic waste. To put things into perspective, any food addition or fish excrement is broken down into ammonia. With a robust nitrogen cycle in place, the nitrifying and denitrifying bacteria will make short work of converting that ammonia into nitrate.

In a new tank set up, there may be an ammonia spike cause by the bloom. However, the nitrifying and denitrifying bacteria, which are slower to reproduce, will soon catch up and convert that ammonia. If you are concerned by the level of ammonia in your tank, it is a good idea to nutrilize it using a product like Seachem Prime.

Seachem Prime Fresh and Saltwater Conditioner - Chemical Remover and Detoxifier 500 ml
  • POWERFUL TREATMENT: Seachem Prime is a complete and concentrated conditioner for both freshwater and saltwater fish tanks, working hard to remove chlorine and chloramine.
  • REMOVER: Seachem Prime immediately and permanently removes chlorine and chloramine, successfully allowing the bio filter to remove ammonia, nitrite, and nitrate while they are detoxified for 48 hours.
  • DETOXIFIER: Seachem Prime effectively detoxifies ammonia, nitrite, and heavy metals found in the tap water at typical concentration levels, providing a ideal environment for your betta, tetra, or other fish.

How do you get rid of bacterial blooms in saltwater?

In a new set up, you can choose to ride it out. If however, you intend to purchase and install a UV sterilizer at some point, then this would be the perfect opportunity. The installation of the UV sterilizer will get rid of the heterotrophic bacteria in a couple of days.

In a well-established saltwater tank, improve your tank husbandry and siphon the substrate to remove excessive organic waste. Then install a UV sterilizer to clear your water and prevent a bloom from happening again. A great product to help in clearing away organic waste is DrTim’s Aquatics Waste-Away.

DrTim’s Aquatics Reef Waste-Away – Natural Fish Tank & Aquarium Waste Management Solution for Dissolving & Cleaning Organic Sludge & Waste - 16 oz. - Treats 480 gal.
  • Waste-Away is a reef safe, aquarium cleaner that dissolves sludge, slime, dirt & waste
  • Solution contains a unique combination of bacteria that dissolve organic wastes & cleans gravel beds
  • Reduces nitrates & phosphates for balanced water, plus helps to extend the life of water filter pads

What is the fastest way to get rid of a bacterial bloom?

The fastest way to get rid of a bacterial bloom is adding a UV sterilizer to your system. By initially placing the pump for the UV directly in your display, you will be ensuring that the bacteria are not being diverted through your filtration before they encounter the UV. Instead, they are being directly drawn through the UV for a quicker result. Once the bloom has passed, you can set the UV up in your sump, or away from your display.

Will a UV sterilizer clear a bacterial bloom? Without a doubt, yes!

In my opinion, a UV sterilizer is a very valuable addition to any reef tank. Not only will it get rid of a bacterial bloom quickly, they also help the water stay crystal clear and control other unwanted algae like dinoflagellates and chrysophytes. They are also fantastic as a method in the control of fish diseases like marine ich.

Will a bacterial bloom deplete oxygen levels in my saltwater aquarium?

Heterotrophic bacteria utilize large amounts of oxygen during a bacterial bloom; therefore, it is vital to provide additional aeration. This could simply be pointing your wave makers to the water surface to create water surface agitation. This will ensure that you increase the potential for gaseous exchange. Ensure that your skimmer is on at all times, as your skimmer is the main oxygen input source in your aquarium. If you see your fish spending more time at the water’s surface, add some air stones to inject oxygen directly into your water column.

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