I got a few Squirrel Cage fans for free. If you go to heating and cooling store they throw out there old junk from installs in the trash ask if you can pull a fan off . I use inline's they work the best. Always go bigger than what you think you need.
The more air you put in your water the better off you are. For exp look at http://www.ezclone.com/products/120-unit-cloning-system/ the roots don't sit in the water and there still adding air.