For me, all liquid tooltips (exept for buckets, which are items) are not working.

src\main\resources\assets\biggerreactors\lang\en_us.json

Not working:
"fluid.biggerreactors.liquid_obsidian": "Liquid Obsidian",
Working example correction:
"fluid_type.biggerreactors.liquid_obsidian": "Liquid Obsidian",

Maybe it's just because of a config issue with my custom modpack.