hi there and welcome
I'm sorry to be the bearer of bad news but the tank is very small for the fish you have, as telboy has said goldfish are very messy fish and the filter you have is only recommended for tanks up to 57L, but even then with goldfish you really need loads more filtration. if you do have to keep this tank for now Do not add any more fish!! and you will need to get more filtration. are the fish the long bodied type IE comets?

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