You could try daily water changes. I can't promise it will help but it is one of the few things that really helped for me even after reducing photoperiod, increasing CO2, balancing nutrients, adding floating plants and tearing it down and sterilising everything twice in 6 months... all to no avail, it just kept coming back.
No need to trim the java fern, the leaves will continue to support the plant until new leaves form. The new leaves will be green with a clear tip. Once they get going the plant can double in size within a month. They really like the Flourish Comprehensive but you may struggle to get it to them with the daily water changes.