My question is what should be an advisable bubble flow for minute.

Every tank is different. How much CO2 you'll need depends on how much
turbulence you have, how many plants you have, etc. Use this chart:

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

It will take some trial and error at first.


Leigh

http://www.fortunecity.com/lavender/halloween/881/