Theres no light sources there, kinda weird

What other mods do you use?

Is that glass tube connected to the surface, or close to it? If so it might be just skylight being able to pass through the glass which is transparent but not through the water which makes skylight loose 1 each block of depth

The tube does rise up over the water, so that might be it

Could you test this with normal sodium and or vanilla to see if the problem persists, if it does then it's just skylight like Ztereo said.

Yep, I tested it without indium and the same thing happened

Yep, I tested it without indium and the same thing happened

So this is not an indium bug and should be closed.