Please tell me that you don't have all of those fish in a 20 gallon... Your bio load is way too heavy, some of those fish are going to be fast growing huge. I've only skimmed through the responses, but if your tank is not cycled with that kind of load, you will have casualties. Then you will have more casualties of the smaller species as your larger species grow. The kissing gouramies and bala sharks are definitely going to outgrow the 20 gallon before you know it. Please return them to the store, or rehome them and get fish the appropriate size for your tank.
Good luck,
Mary.
Good luck,
Mary.