45 tanks ... what size?
45 5 gallon tanks would be vastly different from 45 90 gallon tanks.
A better way to evaluate your situation is how many "drops" (airline outlets into the tanks) do you want/need and at what depth?
If you're thinking 2 drops/sponges per tank and most of the drops are 18" or less, you'd be better off with a linear piston pump IMO. Especially if the air source is going to reside in the same room since linear piston pumps are much quieter than blowers. A LPH100 from Jehmco would be a good fit in that case:
http://www.jehmco.com/html/lph100.htmlIf you have deeper tanks, you can cheat the pressure problem a bit by raising your sponges in-tank.
If you have deep tanks, need 120+ drops, a blower would be better. As already mentioned, talk to John at Jehmco and he can get you setup with the right equipment.