Summarize:

This plant will grow just fine in the front of your aquarium, but it’s likely to block your view of your fish! Instead, consider using it as a background piece, or let its beautiful leaves become a central focal point that your fish can circulate around.  A Java fern rhizome generally grows in one direction, and can reach about 6 inches (15 cm) wide. The leaves can grow to about 12 inches (30 cm) tall. Because of their size, Java ferns are best for tanks that hold at least 10 gallons (38 L). Java ferns are hardy plants that can tolerate nearly any typical aquarium environment. However, they are more likely to thrive under the following conditions:  a tank temperature between 72 and 82 °F (22 and 28 °C). a tank pH between 6 and 7.5. low to moderate tank lighting. Many Java ferns can get adequate nutrients from their aquarium surroundings and will never need a fertilizer. But, if your fern has shown little to no signs of growth after a month, try adding a liquid fertilizer that includes iron.  Choose a liquid fertilizer that suits your aquarium conditions, and follow the instructions for adding it to the tank. You may, for example, need to add a small amount of liquid fertilizer into the tank each week with a dropper. The fish can remain in the tank while you add the fertilizer. Black veining is normal on Java fern leaves, and black bumps on the leaves are signs of new growth, not disease. However, if your fern has brown spots on the leaves, or if the leaves start to get mushy or disintegrate, you do have a problem. Brown rot is typically due to too much light, too few nutrients, or too much blue green algae (BGA). In the last case, keeping the tank clean and increasing the nutrient levels with a liquid fertilizer may improve your fern’s health.
Locate the fern in the middle or back of the tank. Adjust the temperature, pH, and lighting if necessary. Add a liquid plant fertilizer only if necessary. Make adjustments if you see brown rot.