Like what a few others have stated I would get some coolant from Subaru. The funny thing is, I don't run any Toyota lubricants (or Subaru) unless it is coolant. You can't go wrong with going to the source of who actually built the engine. Toyota did the fuel management system so that doesn't say much on the rest of the engine lol.
Edit: I currently run a FBM radiator to increase the amount of coolant I have. My reservoir is usually low to empty until I drive the car and the engine gets hot. After cooling the radiator/engine pulls my coolant back into the radiator. Just watch your temps
Hope this helps.