I have the same problem. I assumed they don't like my water - maybe certain minerals/levels don't agree with them - and that my lights are too bright? There's lots of other plants out there, so I just keep the ones that are happy in my tanks.
Don't be embarrassed, we are all here to help each other! Most of what is on the net about java fern is trash such as it only grows in dim light and in water temp of 68 to 78 degrees blah, blah... Do you have the roots attached to a log or rock? That is the best way to get it started. Contrary to popular belief, they can grow in the substrate at their will so let it extend the roots down to establish itself. I have this plant growing in one of my ponds outside in the sunshine (filtered) emersed. Do you know the source of the plant such as another hobbyist or was it acquired from a pet shop? This plant will grow unless you have really awful water which I doubt.
I get them from Etsy. I usually superglue the rhizome to pebbles. That way I can move them around if I want. Although my most successful ones are glued to a piece of driftwood.
I have soft water. What about vice versa, from hard water to soft water? I assume that could be a similar problem.
I try to find a balance. I don't want my fish getting blasted with too much light but try to provide an adequate amount for the plants. Most of my other plants grow well enough. Is too much light an issue with java ferns?
Never do that. I always superglue them to something.
Mine are growing in the same soft water and lighting conditions too, I dont have to fertilize them at all. I credit my RO/DI water for making a difference.
