it may not mean anything! clear is normal.

how can a man stop bacterial vadinosis?

a man cant stop it! some women can get it by simply douching. the women rinses the good bacterial out and allow the bad bacterial to spread.
when i used condoms for five years i never gotten a yeast infection or anything else. it's when i would have sex without a condom that i was susceptible to bacteria infections.
so you could use condoms when you have sex.