How To Fix Cloudy Aquarium Water

It happens to the best of us. In the morning our tank was crystal clear and we could see every detail in our fish from across the room. Yet when we get home we see it. The heavy fog over our tank, looking dirty and dangerous. We buy tanks to decorate the room, not to have a dirty cloud.

Too many new owners give up right here. If the tanks cloudy after a week of owning it then clearly the hobby is just too hard. But they are far from the truth, as this problem is short lived and signifies your tank is on the right path.

So how can new owners fix this problem? our first step is to identify what exactly is happening in your fish tank. You don’t get an engine change when your car makes a weird noise do you? Of course not, you find out what the possible issues are because knowing the problem leads to solving the real issues.

As you add new fish or filter media from existing tanks, microorganisms begin to spread throughout the water. Normally our household wanted is treated with chlorine to keep these at bay. While setting up our aquarium we remove the chlorine from the water, as fish will not survive otherwise. This allows the bacteria to begin breeding without limit, feeding on extra fish food and waste.

Bacteria grow exponentially, meaning you may only start with a dozen or so specks of bacteria. Each day these will re-breed, doubling their numbers until there are too many for your normal fish feedings to support them.

This is where the problem actually begins. Once the aquarium can no longer support the rapid growth of bacteria, the new bacteria will quickly die off, letting go of the surface they attached to and floating in your tank. This initial cloud is known as your first tanks “algae bloom”

Dealing With Cloudy Water

While we would love to say you can just put a few drops of chemical x in your aquarium and the problem is solved, the solution is not so simple. For now you can simply do a 30% water changer every day to combat the problem. In order to keep the tank water looking crystal clear we need to actually establish bacteria colonies.

While bacteria and microorganisms are often the cause of your cloudy water they will actually be the ones preventing any further incidents down the line. As explained earlier, the clouds are caused by dying algae. Once algae begins dying, the left over combination of microorganisms and bacteria must compete for their food. In short, bacteria wins every time. It is just so thin and evenly spread out that the micro organisms cannot hope to win out against a well established bacteria colony.

This is how our micro warfare begins.

If you have not started your tank yet then we suggest two options.

  • Buy a bottle of starter bacteria such as NiteOut from amazon
  • Find used filter media or substrate from an existing tank

By using either of these methods we can “seed” our tank with good bacteria. These are the kind that eat toxins produced by fish waste and extra food, the same nutrients eaten by micro organisms. The difference is good bacteria converts these toxins into much weaker toxins that can take weeks to affect fish. Micro organisms simply breed and produce similar waste, resulting in no change in water toxicity levels.

To seed your aquarium either follow the instructions on the bottle of NiteOut or insert the used media/substrate into your aquarium. Next you will begin feeding your tank as if there are already fish. For those who already have fish you may feed as normal. The waste created by this will feed the bacteria you have added to the tank as well as the micro organisms. The difference is with a seeded tank your bacteria will be growing much faster than the microorganisms that cloud tanks.

Preventing Cloudy Water While The Bacteria Grows

Ok so we have established that you need to let the bacteria in your tank live if you want the clouds to go away and never return, but how does that solve your problem now?

Simple. Because the dead bacteria and microorganisms are now floating around and clouding your tanks you can easily remove them with water changes. This will make your tank water less foggy but not completely clear.

To prevent strong, dense fogs while your tank establishes a good bacteria colony you will need to follow a few steps.

    • Be Patient

We know this is the last thing you want to hear, but if you are to have a clear tank for years to come, you will have to deal with a little haze for one to three weeks

    • Respect the golden rule: one inch of fish per gallon of water

While frequent water changes can allow for more fish to survive in the tank, almost no owner will actually do two water changes a day for 5 years just to keep an extra three fish. Be realistic and get only the fish you can take care of.

    • Perform regular water changes

Think of this as your practice for the normal maintenance your aquarium will require. Daily water changes allow you to quickly learn the fastest and easiest way to clean out your tank, meaning once the problem is gone you will have learned a great deal on keeping your tank spotless.

    • Do Not wipe the glass every day

Microorganisms swim around in the water, actively hunting for food. Some will settle onto the glass from time to time, meaning you can keep a bit of them out by wiping the glass. Bacteria on the other hand will almost exclusively stay put on your surfaces. For this time only we urge owners to let the algae sit on your glass. Once the fog ends you can wipe off portions of the bacteria day after day. Wipe too much and you have just undone all the growth your bacteria has worked so hard to achieve.

    • Refrain from over stocking your tank

In my youth I have worked at pet stores. While many of you will ignore our warnings about buying too many fish at once, every guide available will tell you the same. Limit your new fish to one fish a month, at most 3 in a month if they are small schooling fish. Going from no fish to ten fish will guarantee you get a long lasting algae bloom as your tank is unable to keep up with the waste they produce. Unless you perform two 30% water changes a day, expect large additions of fish to die off rapidly.

We cannot stress this enough. Bacteria saves fish. Please give it time to grow or your fish will have no hope of surviving.

    • Remove uneaten food and dead fish as soon as possible

After feeding your fish some flakes may be left over. The mistake too many owners make is feeding extra to feed the bacteria too. The thing is your bacteria eats your fishes waste, meaning you have already fed them. Limit fish feeding to two small feedings a day on a normal tank, limiting to every other day for clouded tanks. Your fish can hunt the micro organisms so don’t be too worried.


Remember maintaining water quality isn’t just a one time deal. After kicking your cloudy water problem out the door it is up to you to keep the tank safe and clean. Perform regular water changes and watch for new algae blooms. An ounce of prevention is worth a pound of repair.

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