Definitely, do not add either baking soda or washing soda, with those values. If you raise the pH with washing soda (soda ash, sodium carbonate, pH Up, etc.) while having a CH=500, you're likely to precipitate calcium carbonate and make your pool look like milk.

You *can* use cal hypo, but add it via the skimmer after making SURE -- 100% sure -- that there is no feeder or gizmo anywhere between the skimmer and the filter. Also do NOT add CYA immediately after adding cal hypo, and do not add cal hypo within 3 days of adding CYA to the skimmer.

BUT . . . raise your pH, ASAP. You could use caustic soda, but that stuff is nasty to work with and usually expensive for consumers. Instead, go to Walmart and clean them out (up to 20 boxes): http://pool9.net/borax/ (Actual box is now mostly white, not green.)

Add boxes, 5 at a time, to your skimmer. Do it slowly, with the skimmer running. Do NOT choke the skimmer: borax can 'meld' together and form a solid, hard-to-dissolve, lump in your pipes if you do. Wait 4 hours to retest your pH.