Symptoms

• Java ferns often display brownish or blackish spots or areas that gradually spread throughout the leaves, eventually covering the plant. The plant will then deteriorate completely. Sometimes, after the dead leaves fall, small buds will grow back.
  
  

Causes

• One potential cause of java ferns turning black is poor nutrition. Just as with houseplants, aquarium plants need proper nutrients to thrive. Nitrate levels should be 10 ppm, and phosphate levels should be 1 ppm. Calcium and magnesium shortages can also cause java ferns to turn black. Another cause may be poor growing conditions when java fern is buried in substrate where it cannot receive proper nutrients. Older plants naturally die, and this is often what it looks like.
  
  

Nutritional Solutions

• If nitrate levels are too high, avoid overfeeding fish, and use a reverse-osmosis deionizer or nitrogen-removing filter to remove nitrates from tap water. If phosphates are too high, try using a phosphate-reducing resin, which you can find at aquarium stores. For either problem, skimming the tank more frequently will help. To add more calcium and magnesium, add calcium carbonate (CaCO3) to the tank. It can be found at nurseries, hydroponic stores and aquarium stores. Finally, attach java fern to a piece of floating wood or a rock so it can receive nutrients from the water.
  
  

Other Solutions

• When java fern turns black, don't panic. Instead, have patience. Remove the old or damaged parts of the leaves, and allow new buds to form. Once the small new plants begin to sprout, gently separate them from the larger java fern and place them where you like in the aquarium. If you wait, they will actually detach on their own and find a rock or piece of wood to grasp onto. They will grow slowly, but eventually they will be viable plants.