Without a filtering system or poor filtering ability, it is difficult for you to raise several fish.
The landlord likes to raise fish, but you can pay attention to our company's latest patented fish tank, which is known as the strongest fish artifact in history. This is not bragging, but based on facts. Look at the size of this tank 62, which is similar to yours. Koi fish 1 piece over 30 cm, koi fish 3 pieces over 10 cm and goldfish 2 pieces. These fish have been raised for half a year, and they have only changed water and washed cotton once. Every time I see the pile of high fish poop behind the filter, I feel a sense of accomplishment.
You should probably understand why water can be kept so well and fish can be kept for so long.