It may be clear now, but if you let your chlorine drop to 0 with a CYA reading of 60, then you probably have something starting in there that hasn't "bloomed" yet. My advice is the same. Go ahead and shock the pool. It may be that doing so one time will be all that you need and you'll find that you don't lose more than 1ppm of chlorine overnight. If that is the case, then you'll be good to go as long as you don't let the chlorine drop again. But, my opinion is that it is better to go ahead and shock a pool that looks clear rather than chance it and end up with a green pool.