Angie, to raise the Alkalinty, we go the cheap route, baked baking soda, I add 4 tsp's per day any time the alk drops below 9dKH, I just mix it into a 2 gallon top off and drip it in. (just until I get the new top auto top off built)

By baking it, you remove the majority of CO2 from it, which in turn helps reduce the raising effect on PH. I do large batches at a time (several boxes), spread it out on a cookie sheet and bake @450 degrees for about an hour, store as airtight as possible (gallon ziplock bag works great).

I understand washing soda will work as well, but I haven't looked for it around us so haven't tried it yet, not sure what the effects on PH are either.