Sorry if this is a shocking question that has an obvious answer. I've never had a vacuum before. I keep hearing about them. Do you have to vacuum your tank? I keep hearing horror stories of people sucking up their fish and the fish getting shredded to death and now I'm horrified and don't want to have to use one. Also, what's the difference between a siphon and a vacuum? How does the vacuum or siphon not suck up the rocks? Thanks!