You would be surprised how much beneficial bacteria and unwanted debris a sponge filter can hold! Back when I was new and clueless to the hobby, my weak sponge filter kept 3 adult and 5 adolescent guppies in a 2.5 gallon alive and healthy I'm sure it can handle a goldfish in a large tank!
They would keep essential bacteria on your tank to ensure a heathly tank, so when you change the filter you just have to gently wash the bioballs and put them back in, so you don't have to restart the good bacteria needed for you tank.
Get a big air pump and use two of the large sponge kits. This way you can alternate cleaning them. Remember to pretreat your water with API stress coat before you add it to the tank when changing water. Filling the tank and then dosing exposes your sponges to chlorine. ......and yes I said API stress coat and not Prime. API puts aloe in the ingredients which is one of the secrets for keeping gold fish healthy.