I can only speak based on what LLL reptile told me over the phone, but all of their large fixtures use electronic ballast so it's safe to use T8 or T12. I only asked about the one I ordered (30" fits 24" bulb) and larger hoods, so you should call them and ask if yours is magnetic or electronic ballast. If magnetic, ask T8 or T12 and use appropriate bulb. Cheers.
With the hoods from LLL - you might have to wait through a good minute or so of flickering before the light actually comes on. I'd give it another shot.