Filter Suggestions

So here is what I am thinking I will do. After careful research I have decided to buy a Dynaflo 20-50 because it gives me a lot of options. The problem is now that I have all these options which do I go with.... hmm. It will be difficult to get ahold of replacement cartridges for this and so I was wondering if I can just replace the fuzzy filter stuff and use the same filter pad again or maybe put extra filler before the pad and replace that? I have also heard that this model is not great when it comes to bio filtration so I was planing on throwing some bioballs in there since there is a lot of room. Maybe some carbon too? the filter pads have powdered carbon so i might need to add extra?

nevermind! I have had a change of heart and I am going with an Aquaclear. thanks for all the helpful suggestions..........

The pleco and rainbow shark are both leaving on tuesday. the gold fish has been in that tank for 2 years and is just fine. he started out as a feeder fish and I kept him. Maybe you suggest that I should spend the money to buy a 20 gallon tank for a 35 cent feeder but I am not going to be able to do that. BRING ON THE JUDGEMENT ANDTHE LECTURES! I don't remember asking you if my tank was overstocked though.... hmm I seem to remember asking about filtration but since you want to give me your opinion why don't you go ahead and answer my question!