The leaves of the Java Fern can grow as tall as 1-foot in your fish tank. If you are having problems trying to get this plant to grow big, then you can check out this troubleshooting article from Aquarium Blueprints.
1. For the first step, you should make sure that you are keeping the Java Fern within its recommended temperature range. The good news is that the plant is able to tolerate a wide range as anywhere between 68°F to 83°F (or 15.5°C to 28.3°C) should be fine.
2. Furthermore, you should also make sure you are using the right aquarium lighting. While this plant has a low light requirement, it does best under lights that have a 6700k spectrum.
So, if your lighting fixture offers this spectrum, then we recommend switching over to it. Otherwise, you can try getting a new light bulb and/or fixture to see if the Fern ends up growing at a faster rate.
3. It is important to note that you shouldn’t bury the rhizome beneath the substrate as it needs to be waterborne. Otherwise, the leaves may have a hard time growing.
For the uninformed, the rhizome is the thick green root that has smaller and thinner black roots, as well as leaves, growing on it.
4. If you just added Java Fern into your tank, then it may take a few weeks, or even months, for it to fully acclimate to your fish tank.
During this process, the plant may die-off and grow new leaves. These new growths should be better acclimated to your water parameters and, therefore, should be able to eventually grow bigger.
5. If you don’t have enough nutrients in your tank water, then the Java Fern may end up being limited when it comes to reaching potential.
If you have a high bio load, then the organic wastes and decomposing food should provide enough nutrients for the plant to grow without any issues.
If it remains small, then the bio load may not be enough. In this case, you can try using a liquid fertilizer to speed up the growth. When we were having trouble with Java Fern, we started dosing Seachem Flourish, which helped get it back on track.
6. If you have other aquarium plants in the same tank, then the Java Fern may be getting outcompeted when it comes to nutrients intake. Some of the other plants may also be blocking the light needed by the Java Fern in order to keep growing.
In these cases, you can try moving the other plants into another tank if possible. By doing so, the Fern will be the only one remaining in the current aquarium, which means that it does not have to compete when it comes to lighting and nutrients.
Once the leaves have grown to your desired size, then you can try re-introducing the other plants in the same tank.