Wow, yeah - I'd have to agree - go completely the other way on the aperture as F22 at night is simply not what you need when you are trying to get a faster shutter speed. I can't think of any reason you couldn't shoot even wide open apertures - with a 30mm focal range from that distance, there won't be any issues with depth of field - I've shot the castle handheld with a 30mm lens on APS-C sensor at F1.8 and had everything in razor-sharp focus.
If you use your biggest aperture (dont' know what lens you were using, but assuming kit lens you should be able to get F4.5-5.6ish. With ISO200, 400, or even 800, you'll get a lot less noise, and can still pull off shutter speeds of a second or so to capture the quick light displays. Also, just to be sure - were you using a tripod? Your 2-second shutter speeds are awfully slow for handheld, so I'm assuming yes - but that is another obvious suggestion if not....and when shooting short exposures like that - 1-2 seconds - mirror vibration can very much come into play, so I'd recommend taking those shots on a tripod with mirror-lock-up engaged.
I think I'd try Tv setting at 1 second, let the camera choose wide-open aperture and use Auto ISO - see what ISO the camera picks. If the camera tries a higher ISO and a slightly smaller aperture, then take that setting as a baseline, switch to manual mode, and set the aperture to wide open and lower the ISO by the same number of stops as the aperture you adjusted.