Can't help you with the food, but may I ask where you acquired the catfish, what size and pricing? Thanks.
I'd like to know about the catfish also.
Whereabouts near Tucson?
I know that Taylor Feed, way out on Golf Links at Harrison, carry catfish pellets...at least they did. About three years ago when I thought I'd be getting catfish, I got a 50 lb bag for about $35 I think. (I decided against catfish because of all the guv'ment permit/fee stuff required.) So if that's too far to go, contact your local feed stores to see who carries it.
I get Pond Pellets for my tilapias at WalMart...10 lb bag for around $20. The pet stores want way too much for the same bag. EcoGrow on the NW side may be able to help if you're on that side; they're always advertising on Craigslist too...they deal a lot with aquaponics.
I just looked at your profile and see you are in McNeal...a search for Purina AquaMax catfish food shows there are two feed stores you might call:
TRACTOR SUPPLY COMPANY 1871 215 W 9TH ST DOUGLAS, AZ 85607 Phone No: 615-366-4600 Fax No: 615-366-4700
HIGH LONESOME TRADING CO. 10343 HWY 191 ELFRIDA, AZ 85610 Phone No: 520-642-9343 Fax No: 520-642-3831
Here's website for the feed: http://aquamax.purinamills.com/