can I use a regular power filter or do I have to go to canister with the over flow. because I don't want the hasle of alterating the tank.
For a 20 gallon tank a standard HOB power filter would be fine. You may decide you want to upgrade later, but it is not strictly necessary. Canisters are pretty easy to set up anyway...no need to alter the tank.
thak you very much. is there any special filter compounds I should use or is sponge charcole and phosphate filters ok