The more you feed, the faster they growth. Feed them every third day is about right.
Be careful with feeding the silverside. As long as your siverside is fresh and not smelly (smelly=spoiled) it is fine. However feeding the spoiled food can and will kill them.
I don't use silverdise. Too expensive and often they were spoiled and reeked by the time it get to me. Fish or shrimp for human consumption are much cheaper and better.