What kind of pool do you have? If it's plaster or concrete, then Ca of 230 is ok but I wouldn't let it get lower than that. If it's a liner pool, then the Ca reallydoesn't matter, as long as it doesn't get high enough to cloud your water. I'm at work right now and don't have access to my chem caculator but when I get home later I'll figure the answer to your CYA question if nobody beats me to it.