We have a Hayward S220 Sand Filter and have had to remove the sand to check for a problem with laterals and center pipe. We were concerned last year there wasn't enough sand when we put the new in (although I would have thought we put the right amount as we were putting new(: ) Anyway, we removed some sand because of scaling and crud on the top. We bought an extra bad, but aren't sure how much to put back in. There, of course, is an amt given in lbs but there is no way to tell a level where the sand should be in the tank. Any thoughts on how to know how much sand?