How do u know when your java fern is sick?

how would u know when your java fern is sick or dead or very bad that it can kill a fish.

How do u know when your java fern is sick?
Java fern will start to turn brown as the older leaves die off. New leaves should be forming. If not, you might want to try some aquatic plant fertilizer. If you see brown leaves, you should remove the brown pieces, and test your tank for ammonia, nitrite, and nitrate. This way you will know if the water is turning bad.