hello there, 28x19cm is a small tank. Small tank is unstable and fish won't survive long in those tanks. But since you are keeping feeder gold fish, then it does not matter. No need to buy sponge filter too, save money. Get a feel of the hobby if it is the right one for you.
If you want to start a fish tank or have decided on it, then can google "recommended tank size" and "cycling your aquarium" in the future.
Take care.
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