Ok I am leaving to go on vacation for 5 days (Wed.-Sun.) and I have seen these weekend feeders for sale that you drop in your tank and is supposed to feed them while you are gone. I have never read up on or used one of these and wanted you guys opinions on these. Do I need one? If so how many? (with 5 gold barbs and 3 cories in a 20g reg.) thanks for all opinions.