Don't be silly, course there was water in it. The pump was working & there was flow, it just was'nt getting as much water as it needed.
I'm still thinkin how to make up the LED plug. Might have to get a short length of clear perspex bar, thread it with a 1/2" die & turn it to shape on a lathe. Bit expensive for just a plug though, with the 1/2" die costing me £15 alone.