How often should I clean my goldfish aquarium?

I have a 40 gallon aquarium which has a 55 gallon filter on the back and a sponge filter on the inside. (the filter that came with the 40 gallon didn

I have a 40 gallon aquarium which has a 55 gallon filter on the back and a sponge filter on the inside. (the filter that came with the 40 gallon didn't work right out of the box. The one I'm using now is probably better anyways) and I have 3 small comets, around 2-4 months old. How often should I clean the aquarium?
I do have plans to build them an outdoor pond, but not until late spring/early summer.

or:I have a 40 gallon aquarium which has a 55 gallon filter on the back and a sponge filter on the inside. (the filter that came with the 40 gallon didn't work right out of the box. The one I'm using now is probably better anyways) and I have 3 small comets, around 2-4 months old. How often should I clean the aquarium?I do have plans to build them an outdoor pond, but not until late spring/early summer.

or:I clean out algae and rearrange things in my tank every month, and I do a full clean every 2 months. That's what I suggest.

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