The washing soda can be used to raise both pH and alk, so it would be okay to use it with your current numbers. Better get some chlorine in the pool, though, because running a pool with CYA of 100 and chlorine level of less than 8 ppm is an invitation to algae! If your chlorine has been low for more than a day or so, I would go ahead and shock the pool to make sure you don't have something already trying to bloom.

Janet