Yellow or Brown Aquarium Water: Causes and Solutions

Dirty Aquarium Water

Aquarium water is generally pure and colorless, however it might get clouded or coloured from time to time. Although there are times when unexpected yellow or brownish colored water is not a concern, it is typically an indication of problems. To ensure that your aquarium habitat is safe for your fish, check any yellow or brown water right away to find the source and, if necessary, rectify it.


Cloudiness is caused by bacterial overgrowth, often known as bacterial blossom or bloom. Although the water seems gray or milky, bacteria do not color it yellow, brown, or even green. The problem is dissolved organic debris rather than bacteria if the water takes on a noticeable yellow or brown colour, thus bacterial bloom is ruled out.

Keep in mind that many concerns may be present at the same time. If your water is coloured and also highly foggy rather than clear, you may have a couple of problems on your hands.

Dissolved Organic Compounds

Dissolved organic compounds are a common source of tinted or hazy water, but what does it mean? Organic substance that has broken down in water is referred to as dissolved organic compounds. Fish waste, uneaten food with rotting plant pieces, or even dead, decomposing fish parts might all be culprits.

All of these sources can cause organic molecules to dissolve in water, altering its composition. These chemicals have an effect on the health of your fish. These substances will lead to water chemistry changes that are hazardous to fish over time. Organic chemicals dissolved in water produce unpleasant scents and make the aquarium appear less appealing.


One reason of brown or yellow water is the presence of tannins, which is typically not an issue. Driftwood contains tannins, which will leach into the aquarium water over time, turning it yellow to brown. Tannins soften and reduce the pH of water. This may be beneficial and even encouraged for some fish. This is especially true for South American fish, which require soft acidic water to survive and reproduce.

Troubleshooting Steps

A few indicators can provide clues as to the root cause of water discoloration and resolving the problem.

The pH, ammonia, nitrite, and nitrate levels in the water must all be determined first. Examine the tank thoroughly as well. Do you see a lot of trash? Are there any dead plants, uneaten food on the substrate, or perhaps a lost fish that is rotting somewhere? Is there any driftwood in your tank? Is the filter working properly? Is there any froth on the surface of the water? Does it make foam if you put some water in a closed container and shake it? Protein wastes in the water are indicated by foam.

Fixing the Water Discoloration

Once you have completed your tests and observations, you can determine the next course of action.

  • Tannins: An acidic pH along with driftwood in the tank is a strong indicator that tannins have leached from the driftwood. This is not a problem unless you are keeping fish that require a significantly higher pH. If driftwood is the cause, the tinted water will clear over time, as the tannins in the driftwood will eventually deplete. If you keep fish that require an alkaline pH, consider changing your aquarium decor to something that will not lower the pH.
  • Biologicals: If the ammonia or nitrite levels are elevated, then the biologicals or natural bacteria in the tank are not stabilized sufficiently to keep toxins in check. Because both ammonia and nitrite are potentially lethal to fish, take steps immediately to lower them. Your quickest course of action is to do a large water change. A 50 percent water change will dilute the concentration of toxins in your aquarium by roughly half. You should test for ammonia and nitrites after the water change.
  • Organics: If the tank has lots of uneaten food, decayed plants, or possibly a dead fish, it needs cleanup. Likewise, if the water is foamy or foams when shaken, there are a lot of dissolved organics in the water. Clean things up by removing all decaying material such as uneaten food, dead plants, or a fish corpse. Vacuum the gravel and make sure the is running at a normal output. If the filter is slow, odds are it's clogged with debris, which is another potential source of organics.

Do Not Clean Out the Entire Tank

Even if your tank is filthy, don't clean everything all at once. Allow the fish to acclimate to the changes by staggering the cleaning schedule. It will also provide a chance for your biological colonies to recover. You may make problems worse rather than better if you disturb the filter and gravel bed at the same time. Do one, then wait a week before doing the other.

It may take some time to clear up the water, but eventually, it will resolve. Continue a regimen of regular maintenance and the problem is not likely to recur.


"Management of Fish. Merck Veterinary Manual." ;