Gerg, you really shouldn't do any mixing of species, meaning you need to find more of the same newt that you have right now.
30 gallons is a great size and you can do lots with it! You could get some Ghost shrimp, which are pretty entertaining sometimes (as long as you're okay with the idea that they'll end up being a newt snack eventually.)
I would feed more than once a week. I find that the more aquatic, the more often they would like to eat, and the species you have should be mostly fully aquatic (though with several places to come out onto like tall plants and floating corkbark).
You call it a 'california' newt. This is taricha torosa, but taricha granulosa (a rough skinned or oregon newt) is WAY more common in the pet trade. Where did you get this newt? Do you have any photos? Your newt is most likely an oregon newt, which you may be able to aquire via this forum in a few months when people have more offspring.