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.

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.


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.