Mona, you should do a new post when asking a new question - you'll be guaranteed and answer then.
Sand could mean a cracked lateral or a bad seal on the standpipe up the middle of the filter unit where it seals with the multiport valve or just too much sand inside the unit. Sand level should come up to where the filter body starts to curve inwards from it's widest point at the top.
Also, if you just got the pool and filter installed or recently changed your sand, it is sometimes quite normal to see some sand escaping for the first while.

To eliminate fine silt which can easily work it's way through a sand filter only to deposit itself back in your pool, try using a cup or two of DE (2 lb increase in pressure) in your filter (adding it slowly through the skimmer) before vacuuming your pool