When you say "bubbler" I assume you mean an aeroponic mister such as a Clone Bucket? If so, here's what I know.

1. run it 24/7
2. low light at 18/6 (I use 1 bulb in a t-5 panel over mine)
3. Try to keep the water in the "bubbler" about 75 deg. (seedling mat works great, attach the temp sensor to the outside of the bubbler reservoir)
4. Use flowering nutes in the water.. very light strength, I like 400 ppm.
5. Leave your cuttings in rooting compound for about 20-30 sec before putting the cut in the bubbler.
6. Let it do it's thing... about 2 weeks and you should have a good root structure started.
7. Be patient.

Peace,

Farmer Rich