I would take the chlorine up slowly - use regular bleach, bring the chlorine up 1 to 2 ppms at a time. You may not have to go all the way to shock, because you may be getting a cc reading from the sequasol. You can also put a trichlor puck in the skimmer basket if you have a sand or DE filter. DO NOT do it if you have a cartridge filter. Make sure your ph is not higher than 7.2. I would check the chlorine again too, a cc of .5 is not much and it may have been from the sequasol, and may be gone already. Let us know how it goes.