What type of blasting media do people use?

Looks like a big part of my problem is too high a pressure. I was at 100 PSI. Gonna have to try walnuts cause I got some Aluminum work to do. Any idea where to get Walnut blasting media in Canada? Not able to find any yet.

Cley

100 is fine. I blast with 90 so 10 more pounds ain't hurtin nuthin.