Tat's is really the only one close to Ventura, but they did have a new store, I think its called Xtreme Marine, so you can check it out.
Tat's in TO is kind of far from Ventura, about 30mins, but you could do a loop if you want to burn the fuel and go back through TO and then up the 405 to Valencia.
If so, and if you are interested in rare fish and corals, check out reef tank supply as well, they are in Newbury Park. But you must call if you want to see, since they operate from a private location. Still, he has some really nice fish and SPS.