Because you have a vinyl pool, a low CSI is virtually meaningless. Now if it's very high indicating a potential for scale that could be a problem. With winter prep and seasonal refills I don't see that as an issue. The PoolMath APP does a fine job putting initial figures together based on pool type and ideal target levels, but we as pool owners need to review those suggestions to see if any changes are warranted. In your case, I think you're great.