Thanks so far though,
not using Translucent with WaterFilter and checking the texture for Alpha was both right.
Sorry for having caused so much trouble.
I think I have an idea what to do now…
Will use the Smoke.png (has an Alpha channel) when the WaterFilter is on.
This should render a nice looking fire.
Will also try to experiment a little with this idea:
Try to use the gray flame texture somehow to mirror the data and load it as an alpha channel.
(But that’s a very long shot - an idea for later which can be delayed now).
Why the transparent box or particles reveal the background underneath the water is what I’d like to know, but don’t really need by now.
Also, I will try to experiment with the heritage water from here: ProjectedGrid and legacy water effects from jME 2 (MrCoder wrote that for jME2, someone ported it to jME3)
Many new ideas,
Thanks to pspeed for the quick and profound help,
Ogli