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Water clarity in a reef tank

Water clarity in a reef tank

Hi ,Today I would like to share about the clarity of the water in a reef aquarium, and what may be the causes of it and what we can do to make your water crystal clear.

The benefit of a crystal clear tank:

  • Visually happy – Who doesn’t like coming back home and see a crystal clear tank?
  • Better light penetration – Better light absorption by coral ( Higher PAR reading ) due to the clarity of the water.
  • Photographs will look nicer because of clearer water.

Check this out below if you want to know some of the tips & Tricks on taking nice photography in a reef tank.

To achieve crystal clear water, I will list down some of the factors I observe and share with you on how we can achieve it.

Bacteria Bloomed in a new cycling tank is a common cause of cloudy tank.

Bacteria Bloom

Are you cycling your new tank? Did you recently introduce a new bacteria product into your existing tank? Unknowing to many new reefers, these are some of the common factors that cause a bacteria bloom resulting in a cloudy tank. The reason behind it could happen because the population of the bacteria is not kept under control, or there is an imbalance of the bacteria population. We are always told to turn off the skimmer during dosing of bacteria which is indeed true in some aspect as protein skimming will remove some of the bacteria away, but if you are facing a situation of a cloudy tank due to bacteria bloom, it is best to run your skimmer to remove the excess bacteria film in the water.

Luckily, a cloudy tank due to bacteria bloom is not a major concern, as most of the time it will clear up by itself over time. However, in some instances, the bacteria bloom could result in a drop of oxygen level in a reef tank, so do make sure that you keep your skimmer running and provide additional air/surface circulation if necessary.

Common Causes of cloudy tank

  • Bacteria bloom
  • Introducing too much bioload (livestock) at once
  • Overfeeding
  • Overdose of bacteria products
  • Dead livestock decay in the tank.
  • Stirring of sand
  • Heavy bioload – too many fishes
  • Overdose of supplements

UV is one of the commonly used equipment to keep water clear ( Image ; aqua ultraviolet )

What to do if the tank doesn’t clear over time ?

If in the event that the cloudiness does not clear over time, you could consider running an Ultra violet steriliser, ozone, or even use some commercially available supplement products in the market that can help to clear up a cloudy tank.


Little did we know that the quality of the glass can actually affect the visual appearance of the live stock / coral that we see in the tank as well.

The clarity of the glass is affected by ;

  1. Algae on the glass – This is a common problem all reefers has to go through, as algae film growing on the glass will affect the visibility of the tank overall. So do remember to get a good aquarium glass cleaner and clean your glass regularly! I

Different grade of glass actually affects the clarity of your tank – Picture from Aquarium artist showing the difference between crystal glass and normal glass. The bottom one is crystal glass.

2. Quality of the glass – Another important factor that affects the clarity of the tank we see is actually the quality of the glass itself. Do you know that there are actually different grade/types of glass being used for making a fish tank ?

If you choose to use normal glasses, your livestock in your tank will tend to look greener due to the green layer found in a normal glass. However, If you choose crystal glasses, it will look much clearer and less greenish look. Remember the time when you look at the coral from the top of your tank ? Does it appear different from the glass itself?

Another factor is that the thickness of the glasses also come into play of the clarity as well, as the thicker the glass it is, the more greenish it will appear on the normal glass. However, don’t go for a thinner glass just because you wanted to look nice, but a thinner glass will also mean higher pressure load from the water inside, so do remember to discuss with your tank maker about it to select the corect glass thickness to use.

Algae in water column

VERY cloudy, green water | REEF2REEF Saltwater and Reef Aquarium Forum

Like bacteria bloom, the concentrated nutrient in the water column could result in algae bloom which will also likely cause the water to be cloudy in fact green. This often happens when you have very high nutrient level without controlling it.

Here are some of the causes of Algae Bloom

  • High Nutrient in tank
  • Overfeeding
  • Large water changes of unknown water source
  • Lighting in the wrong spectrum (example using plant light)
  • Overexposure to direct sunlight on tank

A possible solution for this includes doing a major water change, controlling your nutrient level by using phosphate and nitrate removal, installing a UV steriliser, running an ozoniser , setting up a refugium, algae reactor or ATS to keep the nutrient in check.

Phosphate can be easily removed with media like ROWAPHOS. Do take note that it work too effectively to remove phosphate therefore it always recommended starting with a small dose. And nitrate can be remove by using products like bio pellets etc..

Other factors that might contribute to a cloudy tank

Overdosing of supplement – Some supplement like Kalkwasser, KH or calcium if is overdose can cause your tank to turn cloudy, so remember to perform a smaller dose separately.

Dosing of supplement that you didn’t know of – Not knowing what you dose is another clear factor of a cloudy tank, and it might even cause causality for your corals or fishes.

Here are some of the solution you can have in place to make your water crystal clear.

Improving your mechanical filtration

A product like the ClariSea SK-3000 Atomatic(GEN2), is a great way to remove fine particles from your water column. Picture from

Old school reefer like me uses filter floss as it is cheap to be disposed of. However, the new age roller filter provide micron size filter matt filteration which allow both small and big particles to be filter away while automatically turning to a new layer of matt once it get dirty. How easy it that !

Running Active Carbon

To maintain crystal clear water, another option is to run active carbon. Active carbon or Activated Carbon is considered a form of chemical filtration. It works by absorbing toxic waste and fine particles from the water column, however, once all it’s pores are filled, it needs to be replaced.

If I happen to miss out on any good options, hit me up and I will research it and put it in this article to share with our reefers.

Supplements that help improve water clarity

There is numerous product in the market that make claims to make the water clearer, personally I have try a few of them and most of them involving introducing another source of bacteria to clear the water.

Microbe-lift special blend is one of the bacteria that reduce your nutrient in water by consuming nitrate.

Vibrant from UWC

Vibrant, “Vibrant is a new revolutionary liquid aquarium cleaner. You can say goodbye to algae, cloudy water and that grungy, dirty aquarium and say hello to that sparkling, crystal clear, algae free, vibrant aquarium you have always wanted! 8 oz. bottle will treat 2,400 total gallons.” directly quoted from the manufacturer. Personally I’ve use this product however it stop my cheato from growing which isn’t what I want. It indeed help my water to be clearer and reduce algae growing on glass.


Another common issue that reefer often face is microbubble in their tank. If you’re not careful with configuring your setup, you will see micro bubble tend to form in your tank which affects the clarity of the water. What are often the causes of this?

  • Return department in sump too low, return pump suction air too when going into the main tank.
  • The wrong configuration of the skimmer, resulting in microbubble escaping the skimmer and entering your return pump.
  • Wavemaker placing to high, absorbing air along with water causing microbubbles.
  • Poor sump design – micro bubble forming in sump compartment.

PS: Clean your lens before taking a picture too, your tank will look clearer that way!