cloudy aquarium water

Cloudy Aquarium Water

Cloudy aquarium water is an extremely common issue in aquariums.  It doesn’t always happen but when it does aquarists are often very hard pressed to find a good solution!  This is because most common store bought solutions really simply will not solve the problem and after seemingly making progress the cloudy aquarium water will just come right back as bad as ever!

Green Cloudy Aquarium Water

The first thing to understand is what causes the problem.  Cloudy aquarium water is actually caused by excessive bacteria in the aquarium water column.  The cloudiness is usually white but can sometimes be green in color if it is caused by single cell organisms containing chlorophyll, the same chemical compound that makes plants green.

Excessive nutrients in the aquarium contribute to the problem but the organisms will be quite adept at absorbing nutrients they need very quickly and once established the problem can be persistent even with great effort, water changes, and maintaining seemingly good water quality.

Clearing Cloudy Aquarium Water With Water Changes and Clarifiers

Clearing Cloudy Aquarium Water With Beneficial Microorganisms

Clearing Cloudy Aquarium Water with UV Sterilization

Cloudy Aquarium Water Video

Clearing Cloudy Aquarium Water With Water Changes and Clarifiers

You can do a 50% water change and the problem will be just as bad the very next day!  This is because the bacteria can reproduce exponentially … doubling in just a few hours or even less.  This is why a 50% water change will be practically useless against the problem.  Water Clarifiers sold in pet stores to address the issue will bind with some of the bacteria and make the water slightly less cloudy but really, it will be even less effective than a water change in the end.  I love API products but I’ve used their water clarifier and it’s just not very effective except in perhaps the mildest cases.

 cloudy aquarium water
API ACCU-CLEAR Freshwater Aquarium Water Clarifier 8-Ounce Bottle

API ACCU-CLEAR Freshwater Aquarium Water Clarifier 8-Ounce Bottle

  • Contains one (1) API ACCU-CLEAR Freshwater Aquarium Water Clarifier 8-Ounce Bottle
  • Clears cloudy aquarium water
  • Clumps floating particles into large clusters that can be easily removed by an aquarium filter
  • Works fast and maximizes filter efficiency
  • Use weekly and when cloudy water is observed in freshwater aquariums only
  • Clear up green or cloudy water caused by gravel and other floating particles in your freshwater aquarium quickly and safely with API ACCU-CLEAR Freshwater Aquarium Water Clarifier. This liquid clarifier combines tiny particles together to form larger clumps so they can settle at the bottom or be removed by your aquarium filter. API ACCU-CLEAR Water Clarifier quickly eliminates cloudy aquarium water caused by floating particles; water will clear within several hours once it is dosed. If cloudiness persists, another dose can be applied after twenty-four hours. Doses can also be administered weekly as part of your routine maintenance. API ACCU-CLEAR Water Clarifier also improves the overall efficiency of your aquarium filter.

So if water changes and common store bought solutions are useless then how can cloudy aquarium water be addressed?  There are actually two separate and fairly different ways this problem can actually be solved.

Clearing Cloudy Aquarium Water With Beneficial Microorganisms

One solution, and our preferred solution, is to introduce beneficial microorganisms that will eat the smaller bacteria or phytoplankton responsible for the cloudy water.  These microorganisms are called rotifers and copepods and are discussed in detail on our Aquarium Microfauna page.  A wide variety of beneficial Freshwater and Saltwater Microfauna can be purchased from my friends at  A single copepod can eat over a hundred thousand bacteria in 24 hours and so are very useful along with rotifers to control cloudy water problems in the aquarium.  Once cleared the tank will have well balanced and established beneficial microfauna in the system and they will continue to provide balance and prevent further issues in the tank.  The will also help control other algae issues and fish disease as well as act as a nitrate and nutrient “sponge” in the aquarium and provide food for corals, filter feeders, fish that feed on small organisms, and fish fry.  Their function as a nitrate and nutrient “sponge” is also useful when used in conjunction with denitrification and will enhance the denitrification process.

Here is a complete package for saltwater aquariums that will most certainly naturally clear up cloudy aquarium water!

Complete SW Aquarium Microfauna kit
Complete SW Aquarium Microfauna Kit for Sale

Coral Reefing Products, LLC
5 Bottle Package – Tisbe Pods, Tiger Pods, Marine Rotifers, Green Phyto(Nannochloropsis Oculata) and Gold Phyto(Isochrysis Galbana)
This Complete Live Package Includes:
600+ Live Tisbe Pods(Tisbe biminiensis)
500+ Live Tiger Pods(Tigriopus californicus)
8 oz. Bottle Marine Rotifers
8 oz. Bottle Live Green Phyto(Nannochloropsis Oculata)
8 oz. Bottle Live Gold Phyto(Isochrysis galbana)

Tiger Pods are microfauna loaded with crude fat and protein. Fish are drawn to the pods swimming through the water. Even troublesome feeders suck as Mandarin Gobies, Scooter Blennies, Anthias, and Butterfly Fish can’t resist our Live Tiger Pods. Tiger Pods can also greatly increase the color and appearance of the fish and coral in your aquarium. Loaded with beta-Carotene, brighter pigmentation will result in most any animals that eat Tiger Pods.

Tisbe Pods are a popular aquarium microfauna food source for many animals, including but not limited to mandarin gobies and other dragonettes, most carnivorous reef fish, young seahorses soft corals & many hard corals. As a colony flourishes in an aquarium, they are effective detritavores, eating excess detritus, fish food, some animal waste, etc., thus helping to clean cloudy aquarium water.

Many often forget the need for live phytoplankton, relying purely on a zooplankton diet. Without a premium phytoplankton diet, the base of the food chain suffers, thus affecting everything in the system. Additionally, many clams, gorgonians & other coral filter out only Phytoplankton, thus zooplankton diets are useless for these particular animals. Besides being a food source that generates the natural food for all tropic levels, Phytoplankton absorbs undesirable chemicals present in many reef aquariums, such as ammonia, nitrite, nitrates, phosphates, silicates, etc.

Live Rotifers and their eggs are a highly nutritious food source for your hard corals, young fish and macro inverts. Packed with protein, our Live Rotifers will promote the growth of most animals in your aquarium.

Clearing Cloudy Aquarium Water with UV Sterilization

Another solution is UV sterilization.  If the addition of beneficial microfauna does not completely eliminate the problem for some reason then UV sterilization will also solve cloudy aquarium water issues.  A UV sterilizer will simply kill the microorganisms creating the cloudy aquarium water problem.  Unfortunately, they can also kill other beneficial microorganism in the tank such as rotifers and copepods.  A UV sterilizer will not act as a nitrate and nutrient “sponge” in the system.  However, it will help control other algae issues and even fish disease.

To keep the Aquarium UV sterilizer from completely sterilizing the tank, it can be helpful to shine a light in the tank at night when it’s dark. A healthy tank should have what looks like dust swirling towards the light. That’s not dust, those are actually beneficial microorganisms that you want in your tank!! If that dust is disappearing too much, use a lower powered UV sterilizer or put your sterilizer on a timer and only use it some of the time.

I recommend perhaps no more than 8 gallons of water per watt when choosing a UV aquarium sterilizer in order to avoid over sterilizing the system. If you are using it to treat cloudy aquarium water then you can try reducing it’s use after the tank is clear. Put your sterilizer on a timer and only use it some of the time. There are a wide variety of aquarium UV sterilizers to choose from for any size tank. Some have replaceable bulbs and for others the entire unit is simply disposable. Either way you will need a new one about every year so keep that in mind.

UV Sterilizers like the one below can help control cloudy aquarium water.

Sun Microsystems In-Tank Submersible Aquarium UV Sterilizer/Clarifier, 9 Watts
In-Tank Submersible Aquarium UV Aquarium Water Sterilizer/Clarifier, 9 Watts

Sun Microsystems In-Tank Submersible Aquarium UV Aquarium Water Sterilizer/Clarifier, 9 Watts

  • Integrated UV lamp ballast
  • Single power cord design
  • Quartz sleeve compression fitting
  • Removal sponge tray

This utilizes a UV-C compact fluorescent lamp that is encapsulated in our unique quartz sleeve that is air tight and allows for a 99% transmission rate to efficiently neutralize disease causing pathogens and organisms that cause cloudy aquarium water. All models of aquarium UV sterilizers include an integrated pump with an adjustable swivel spout and large mechanical pre-filter sponge. A perfect match: We have taken the guess work out of sizing flow rates of pumps to lamp wattages. All models include an integrated submersible pump that is specifically sized for your aquarium which includes a swivel spout nozzle, adjustable flow valve and lamp indicator. Did we mention, you won’t need any tubes or connection fittings its ready to install right out of the box.

We believe that using microfauna to control these issues is preferable and more effective.  However, if a UV sterilizer is used continuously to address cloudy aquarium water, other algae issues, or fish disease then microfauna can be added after the initial problem has cleared up and then only used intermittently to help “polish” the tank up as needed and be kept as a back up solution should it become necessary (such as a fish disease outbreak.)  If the UV is not too strong for the tank then it can be used to help permanently clear up cloudy aquarium water and there can still be enough microfauna for a healthy tank.

If a strong UV sterilizer is used continuously in the tank then you will simply not have the benefits that well rounded and balanced microfauna in the aquarium will provide.  However, it does address many but not all of the problems that microfauna in the aquarium will also solve.  If you do not have any corals, filter feeders, small fish that feed on microfauna and do not care if any small fry survive and you plan to use frequent water changes as your primary method of nutrient control then continuous UV use can be a viable way to keep the tank looking clean and the fish healthy.

Cloudy Aquarium Water Video