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Why is My Fish Tank Water Yellow? (Causes and the Solutions)

One of the goals when having a fish tank up and running is to have beautifully clear water so you can enjoy watching your pet fish swim about. Sometimes, however, the water can start to get cloudy or change color. Common colors are brown and yellow. In this article, we will tackle yellow aquarium water in regards to why it happens and what you can do to fix it.

So the question is, why is your fish tank water yellow? The main reasons why an aquarium’s water turns yellow includes an overabundance of organic compounds, decaying live plants, untreated driftwood leaching tannins, diatom algae or the need for carbon in your aquarium filter. 

I will explain a bit further why each of those reasons could be that your water is yellow and then offer up a few solutions to clearing it up. The good thing to realize, however, is that yellow aquarium water is usually not an issue for your fish’s health and survival. So, if you’re ready to learn more then let’s get started!


Likely Causes of Yellow Aquarium Water

  • Organic compounds accumulating in the tank can be a culprit. Excess food from over feeding, fish poop that never gets cleaned out and decaying (dying) live plants are all possible reasons why your fish tanks water is turning yellow.
  • A heavy bio-load can cause the tank’s water to yellow as well. Over stocking of fish and live plants with a slack maintenance schedule will potentially turn the color of the water and cause a chemical imbalance, which can be deadly for the fish.
  • Untreated driftwood can be the reason as well. If you are using driftwood you found on the shoreline, then you need to treat it before placing into your fish tank. The tannins in the wood will leach into your aquarium, causing the yellow water.
  • Tap water could be causing the problem. I experienced this myself in the 1980’s and 1990’s. Our tap water had a yellow tinge to it. It looked terrible but was safe to consume and bathe in. The yellow is caused by too much iron and or manganese in the water.


How Do I Fix Yellow Water in My Fish Tank?

So, given the four likely reasons your aquariums water has turned yellow, now we can look at how to best remedy the problem. In some cases, having yellow water does not mean there is any danger to your fish, however, you just don’t want to take that chance. Plus, isn’t looking at a nice, clear tank part of the joy of owning a fish tank? I think so. Now, let’s discuss how to fix it.


  • One of the most common issues for any aquarium owner is there being too many organic compounds in the tank festering. Nine times out of ten I feel it happens because most tanks are overpopulated. Over population doesn’t have to be a problem, if you keep a regular maintenance schedule for the tank. You shouldn’t over populate but if you do, here is the solution.
    • If your tank has an excess of food and fish poop accumulating, you need to get rid of it. The best way to do so is to use an aquarium vacuum and perform weekly water changes. Aim to change out about 25% of the water each week. Aquarium vacuums are very easy to use and are a necessity for a successful tank, check out this aquarium vacuum on Amazon. I would also recommend using reverse osmosis water until the problem is resolved. You might not notice a difference in the water color right away, but after a few weeks, it should be fixed with regular maintenance.


  • If you have live plants and don’t regularly take out dead and decaying leaves, you better start. This is another way organic compounds can build up in the water, turning things yellow. Either clean them out as you notice them or take the time when you perform a water change each week to clean dead leaves out of the tank.


  • Next up is untreated driftwood. It’s fun to take aged driftwood from the edge of a riverbed and try to use it in a freshwater aquarium. If the wood isn’t treated, it will almost always release tannins in the water over time, keeping the water a yellow color.
    • The best way to fix this is to boil the wood for a good hour or more. If you don’t want to boil the wood or if the wood is too big to place in a pot, then soak it in a large container changing out the water every week until you notice no more discoloration. Or, do yourself a favor and buy driftwood that is always treated. Check out this driftwood on Amazon already to be placed in your tank.
    • I should note that adding carbon to your filter will help clear the water by absorbing the tannins but it can only do so much. You must deal with the root of the problem, which is the leaching driftwood.


  • Lastly, I have seen firsthand, tap water with a yellow tinge to it. This is typically caused by excessive iron and or manganese. If your tap water is this color, you would hope it is safe to drink and therefore safe for your fish to swim around in. However, it just isn’t enjoyable to watch a tank with yellow water so here are your options.
    • Use reverse osmosis water instead of treated tap water from now on. The only problem with this is if you have live plants you’re not providing them with any naturally occurring minerals from the water, as RO water has everything stripped out. You can use a supplement for the tank, if that is a concern.
    • Next option is to install a filter in your home that helps to strip out the iron, therefore getting rid of the color. I checked on Amazon and found this reasonably priced water filter that should help fix the problem.


Is it Okay If Your Fish Tank Water is Yellow?

It doesn’t really matter if the cause of the discolouring is from tap water or tannins. It does matter if it is because of heavy bio-load or other reasons that can affect the nitrite/nitrate and ammonia in the tank. If that happens, it can be deadly for your fish. So figure out what the root cause is and take appropriate action.


Are there any Other Options to Clear up Aquarium Water?

There are products on the market called water clarifiers that are aquarium fish and plant safe you can use. These products work by causing tiny particles in the water to bond where they become large enough that your mechanical filtration system should be able to clear them out. There are many brands to choose from. I always like to go with the top brands, like this aquarium water clarifier on Amazon, so I know it will work.


Diatom Algae Bloom Will Color Aquarium Water as Well

There is always a chance you have none of the issues described above, especially if the color is slightly brown. Your tank could have an outbreak of diatom algae. This is a microscopic algae that floats in the water and is too small for the average filtration system to clean out.

Luckily, there are diatom filters available to purchase. I have never owned one myself, only considered buying one years ago but didn’t. I have heard throw the grape vine that they work quite well.

I had a look on Amazon and if I was going to purchase one today I would go ahead and try this Marineland diatom filter, as you can’t go wrong with a trusted manufacturer like this.



So there you have it, some reasons explaining why your tank’s water is yellow and some solutions to help you fix the problem. It really isn’t hard to get rid of the yellow water, if you stop to think about why it is appearing in the first place.

I would be shocked if it was because of any reason other than the ones listed in this article.

At the end of the day, if it’s not affecting the quality of life for the fish, then there’s no need for concern. Hopefully this information has helped you. Good luck.

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