Thanks. Yeah, it wasn't the ideal set up. I was just playing about with what I had. I was using the power supply (which isn't my design) for digital Kirlian/corona discharge photography, just thought I'd play about with ionised air.
The half wave with capacitors seemed like a better idea, but I gather a single diode for half wave should ideally be about four times the peak inverse voltage of the input (I could be really wrong about that though), which would be about 60 KV, and it's really hard to find really HV diodes, at least cheaply. I could reduce the voltage or split it, but that's getting a bit convoluted and would probably be even more messy and inefficient, I think I'll just make a multiplier like you linked to.
If I attach the positive to a copper tube with the negative to a single sharp needle positioned at the tubes opening, it belts out a lot of wind, enough to occasionally snuff out a candle - but kind of defeats the point of an/ionising the air, as much of the negative charge gets drawn back into the tube. I probably will go with the voltage multiplier. Thanks for the links! I'll play about with grounding too.