personally i have found the corona discharge ozone generators work well and can run constantly or run timed programes depends on the unit you buy
they are cheaper than the uv generators and produce more ozone than the uv bulbs .. look on ebay many units are available
i did a fair bit of research on these units, 99% originate from china, and are re branded in the USA and Europe and sold at 5x the price in hydroponic stores
these units are in the range of 300mg to several grams ph of ozone produced which is dependent on humidity levels,
i do not have any humidity problems, so these units are perfect for me they are able to remove all smell from the grow room almost instantly
i have read on other threads that smelling the ozone means the unit is producing to much ozone, i would have to disagree with this
if you cant smell the unit making ozone IMO its either not making any or not making enough as i can even smell the ozone produced from my tiny 50mg ph wall socket plugin-unit
the area should be left with a mild chlorine smell, reminds me of the smell of a public swimming pool
ozone does need to be run all the time, or with only short off times or the smell will return