With aquascapes and planted tanks both growing in popularity, we have noticed more and more people reaching out with questions about integrating Christmas Moss in their tanks.
Although Christmas moss is usually a quick, easy, and low maintenance plant to keep in your aquarium that is very beginner friendly, some people can make mistakes that can cause problems.
We commonly see people asking about why their Christmas moss is turning brown with many people who are new to keeping Christmas Moss having this issue so we wanted to publish a dedicated article to help our readers.
Is It Normal For Christmas Moss To Turn Brown?
In most cases, it is not normal for Christmas Moss to turn brown and it is usually an indication of some type of issue within the aquarium that is causing the Christmas Moss to turn brown.
Provided you are able to investigate the potential causes quickly, you will usually be able to correct the issue and have your Christmas Moss return to its normal green color in less than a week.
As with most things though, the sooner you start to try and deal with whatever is causing your Christmas Moss to turn brown, the more likely it is that you will be able to save your Christmas Moss without any long term problems.
Why Is My Christmas Moss Turning Brown?
There are around nine common reasons that your Christmas Moss may start to turn brown in your tank. Some of these causes have very similar reasons behind them where as others are very different but they all over one thing in common…they may your Christmas Moss turn brown.
In addition to the nine common causes that we will cover below, there are also a number of other, less common causes that can also result in your Christmas Moss turning brown.
They tend to be very rare and in unique situations so we will only be focusing on the more common reasons of Christmas Moss turning brown below as that is what the majority of our readers will be having problems with.
Problems With Light Intensity!
One of the number one reasons that Christmas Moss can start to turn brown is due to problems with light intensity in the aquarium.
If the light intensity in your tank is too high, it can cause Christmas Moss to start to turn brown and eventually die off completely.
The level of light intensity required by Christmas Moss can vary depending on the type of aquarium setup that you have.
In general though, we recommend a low to medium light intensity for your Christmas Moss with the plant usually doing very well with a medium light intensity in most aquarium setups.
As a rule of thumb, if you are using a standard aquarium hood with fluorescent bulbs, you should be fine as long as the light is not directly shining on the Christmas Moss for more than 12 hours per day.
In some cases, it may be necessary to provide less light or to shade your Christmas Moss if it is located in an area of your tank that gets a lot of light.
This can be easily done by using something like a piece of driftwood or even a rock to provide some shading for the Christmas Moss.
If you have an aquarium setup with very high light intensity, it may be necessary to move your Christmas Moss to an area of your tank that receives less light.
If you are using LEDs or other high output lights, it is very important to make sure that the Christmas Moss is not getting too much light.
We recommend checking on your Christmas Moss regularly and if you notice it starting to turn brown, try shading it or moving it to an area of your tank that receives less light.
A Lack Of Nutrients In The Tank!
Another common reason that Christmas Moss can start to turn brown is due to a lack of nutrients in the aquarium.
While Christmas Moss is not a very demanding plant, it does require a certain level of nutrients in order to stay healthy and to maintain its vibrant green color.
If the level of nutrients in your tank is too low, it can cause Christmas Moss to start to turn brown and eventually die off completely.
There are a few different ways to ensure that your Christmas Moss is getting the nutrients that it needs.
The first way is to simply use a quality aquarium fertilizer that contains all of the necessary nutrients for plants like Christmas Moss.
We recommend using a fertilizer with a high nitrogen content as this is the nutrient that Christmas Moss requires the most.
Another way to ensure that your Christmas Moss is getting the nutrients that it needs is to add a quality aquarium substrate to your tank.
Aquarium substrates are designed to release slowly over time and they can provide a constant source of nutrients for plants like Christmas Moss.
Many people overlook the importance of substrate for Christmas Moss due to the plant having short roots allowing it to pull nutrients directly from the water in its aquarium tank.
If your Christmas Moss is having issues with the nutrients in its tank though, a high quality substrate can be a great way to supplement the nutritional intake of your Christmas Moss to prevent it from going brown!
Issues With Water Flow!

Another common issue that can cause Christmas Moss to start to turn brown is problems with water flow in the aquarium.
Christmas Moss does best in an aquarium setup with moderate water flow.
If the water flow in your tank is too high, it can cause Christmas Moss to start to turn brown and eventually die off completely.
On the other hand, if the water flow in your tank is too low, it can also cause Christmas Moss to start to turn brown but a low water flow rate is usually not as bad as a high water flow rate and most Christmas Moss can live in a low water flow tank without issue.
Problems With CO2 Levels!
One issue that is commonly overlooked but can cause Christmas Moss to start to turn brown is problems with the CO2 levels in your aquarium.
CO2 is a gas that is naturally found in the air but it is also produced by fish and other aquatic creatures during respiration.
CO2 is essential for plant life as it helps them to grow and thrive but if the levels of CO2 in your aquarium are too high, it can cause Christmas Moss to start to turn brown and eventually die off.
There are a few different ways to ensure that the CO2 levels in your aquarium are at a safe level for Christmas Moss.
The first way is to simply keep an eye on the fish in your tank and make sure that they are not over-producing CO2.
If you notice that your fish are starting to produce too much CO2, you can simply reduce the number of fish in your tank or remove some of the plants that are consuming the CO2.
Another way to ensure that the CO2 levels in your aquarium are at a safe level is to use a CO2 diffuser or aquarium bubbler.
CO2 diffusers and bubblers help to disperse the CO2 in your aquarium and prevent it from reaching dangerous levels.
We recommend using a quality CO2 diffuser or aquarium bubbler if you are having problems with the CO2 levels in your aquarium.
A Lack Of Fertilizer!
Although we touched on using a fertilizer product to help offer nutrients for your Christmas Moss earlier in the article, people often use far too little defeating the purpose of using a fertilizer product.
Always follow the instructions on the label for your specific brand of fertilizer as different products can have different strengths meaning you have to use them in different ways.
If your Christmas Moss is an a low nutrient tank and you don’t correctly dose the fertilizer product you have for the size of your tank then your Christmas Moss is no better off and will often stay brown or get worse.
Tank Mates Eating The Christmas Moss!
In some tank setups, your Christmas Moss might be turning brown is because it’s being eaten by the other inhabitants of your aquarium!
Not all fish eat Christmas Moss though so this is one of the rarer reasons that your Christmas moss may start turning brown in your tank.
Just keep an eye out for signs of small bites in your Christmas Moss or you may even be able to see the offending fish in your tank eating your Christmas Moss as you watch.
Some people do worry about snails and shrimp eating their Christmas Moss but they are usually eating algae growing on the Christmas Moss or the detritus falling off it rather than the actual Christmas Moss itself.
A Lack Of Trimming!
One of the most common reasons that people’s Christmas Moss turns brown is simply because they don’t trim it enough!
Christmas Moss grows rapidly and if you don’t keep on top of it, it can quickly start to turn brown and die off.
Trimming your Christmas Moss helps to prevent this from happening as it removes the parts of the plant that are starting to turn brown and die off.
It also allows you to shape your Christmas Moss into the desired shape which can make it look even better in your aquarium!
A Sudden Change In Water Parameters!
As with most living things in an aquarium, a sudden change in water parameters can cause Christmas Moss to start to turn brown and die off.
One of the most common water parameters that people often change without realizing is the pH level of their aquarium.
pH is a measure of how acidic or alkaline the water in your aquarium is and it can have a big effect on the plants and animals living in it.
A sudden change in pH can cause Christmas Moss to start to turn brown and eventually die off.
Using tap water without a conditioner product to remove the chlorine during a water change can often cause issues in your tank too with Christmas Moss turning brown being a good sign of there being a problem.
Low Water Quality!
General issues with water quality can often cause Christmas Moss to start turning brown in your aquarium.
As we touched on before, a sudden change in water quality can be detrimental to your Christmas Moss so it’s important to keep an eye on the levels of ammonia, nitrites, and nitrates in your aquarium.