I have dozens of plant species, high light and CO2, but this supposedly easy plant has never done all that well until I found out a method I saw on YouTube. Get a thin filter pad (about 1" thick by 3 x 6 or 12") the type that goes in an outside filter that can be reused. (I use and old one for this). Next go to the store and get some cheap clear plastic suction cups 1-2" are fine. Cut holes in the filter pad and insert the small end of the suction cup through the pad, using a small piece of stainless steel wire secure the cup to the pad (this may take a bit of doing until you get it right). Next using thread and a needle sew the java fern rhizomes to the front of the pad (i.e. criss cross the thread over the rhizomes) and stick them to the back glass, high up in bright light. Java ferns do not like to be rooted into substrate, and this method allows their roots to hang in the water. They are basically aquatic epiphytes and will quickly attach to the pad. The pads will look ugly for a time, however the fern pretty quickly covers them. The narrow leaf form looks really nice like this. The nice thing about this method is that you can move the entire "colony" of ferns where ever you want them without disturbing them. Even from tank to tank.