You're missing the point here dude. If you can't get the right filtration (nobody said anything about expensive state of the art stuff), you shouldn't be putting too many fish in that tank, especially fish that grow bigger than the size of your tank itself.
Like I said, you need to properly cycle the tank before you put fish in there and get a better filter. I think an Aqua Clear 110 would be just fine, and you can get one for about $60. It will give you the mechanical and biological filtration you need.
With the fish, some of those guys you just can't keep in a 20 gallon tank, no matter how much filter you have. You really need to research what type of fish your getting and how big they will get, that pacu will be a monster in no time. Nobody's trying to give you a hard time; just trying to steer you in the right direction...