I use a solution of about 50% white vinegar and 50% alcohol (drugstore type.... sorry I forget the usual strength off-hand). I keep this mixture in a dropper bottle and then after diving and showering (or just rinsing ear in fresh water) I lie down, fill one ear with the solution, set a timer for 5 minutes, then turn over and repeat on the other side.
I read this in a medical book aimed for sailors (who would be swimming often in the tropics). I can't say what would have happened if I had not used it, but with using it conscientiously, neither my buddy nor I have had any ear problems. And that included months of often-daily snorkeling in the tropics.
Blue Sparkle
PS: As I understand it, the vinegar kills the nasties and the alcohol helps dry your ear canal. Also, it was stressed that 5 full minutes were necessary/each ear.
PPS: I just remembered that I have heard of some people using an ear dryer. One person I know of uses one called the Sahara DryEar. It's sort of like a little mini hair-dryer that fits into your ear.