Yep .. baking soda will bring pH up. Dissolve it in some water before adding and then wait awhile before testing pH again.
Also, pickling lime ( found in grocery stores) will bring the pH up as well.
1 tbsp in a cup of water ( for a 30 gallon tank ) and add slowly to the tank.
You could also try a water change.... The rapid breathing is due to ammonia most likely and as you and I discussed before, this pH can cause a more toxic ion of ammonia to form.
Also, as the tank begins to cycle, the ammonia will become converted to nitrite, which is very toxic to fish. The nitrite will bind to the hemoglobin in the fish's blood and prevent oxygen from being carried in the blood. In short, the fish begin to suffocate. Again, keeping on top of partial water changes would be a good idea.
If you know someone with a SW
tank, you can ask for a scoop of their substrate to seed the bacteria in your tank.
As for the quick drop in pH, a good buffer can help keep it stable. You might look at getting some Kent's Superbuffer.