You can use dichlor but just be aware that as the CYA level comes up, so does the needed shock level to kill whatever is in your pool. If you haven't already done so, please read the Best Guess Chlorine Chart in my signature. I would also suggest a CYA level of around 50 as opposed to 30. (Actually, maybe aim for 40-45ppm and that way if you overshoot a little, you'll still be ok.)