First of all, you are naked, and the biochemical indexes of water are not easy to maintain. Therefore, it is suggested to raise a few tropical fish of the family Percidae, which are characterized by wrinkled gills and can breathe air on the water surface, even if they lack oxygen, they will not die. Moreover, they will live well without living erbium and artificial feed. After three years of growth, the medium-sized species are generally around 10cm, which meets your requirements. The fourth price is absolutely cheap, at least less than 10 yuan. Blue dragon, golden dragon, blue star fish, silver dragon, pearl vest (slightly expensive). It is appropriate to raise 4 pairs in a tank with a culture density of 60CM.
If there is a filtration system, if you are sure of the water quality, you can raise red flag fish. The big one is generally less than 12CM, with bright colors and red. It's very beautiful, but you have the habit of jumping. You have to cover the fish tank, and Kimmarie is also very good. Both kinds of fish are viviparous. It's enough to buy three pairs, and there will be many fish babies, which is also very fun. If it is mixed with bass, it should be purchased with the space required by the following fish, and only three pairs are raised.
Personally, I think it is more appropriate to match a small amount of aquatic plants.