Not difficult to adjust. I actually just re-did mine as the old one had to have the pump dialed back so as not to overflow the tank. Made with 1.25" pipe and drilled 5 holes at one level, then 3 holes below that level. Started it wide open then moved the bell housing up til I found the sweet spot.
If you don't have a dremel to grind out the inside of the bell, a sharp knife works well enough just shaving away a bit at a time (good to do during a TV show since it can take a while).