Just for closure I thought I would update. Whilst lowering lights didn't hurt, it didn't help either. And I don't have control of light in one of my tanks, which is almost entirely daylight-driven during the summer. However I'm happy to say - no - shout: I AM NOW SUCCESSFULLY GROWING JAVA FERNS!
Playing with ferts has sorted me out. I'm reasonably convinced that it was dialing up the potassium that has made the difference (as recommended by a number of forum regulars). However I would caveat that I've substantially changed my overall fert dosing regime as one of the many outcomes of the legendary lean dosing thread, so I also have a lot less N than I used to as well, and I'm using urea in two of my tanks.
Cheers,
Simon
Playing with ferts has sorted me out. I'm reasonably convinced that it was dialing up the potassium that has made the difference (as recommended by a number of forum regulars). However I would caveat that I've substantially changed my overall fert dosing regime as one of the many outcomes of the legendary lean dosing thread, so I also have a lot less N than I used to as well, and I'm using urea in two of my tanks.
Cheers,
Simon