How do you keep a fishes tank clean?

Question

Without a filter.

Answer 1

It is very difficult.  You really cannot.  If it is a tank and not a bowl, you will need to use a lot of elbow greese, with daily wiping and weekly cleaning.  Really if you are housing fish, you should have a filter.  This will also help to keep the water from going stagnant.

Even adding plants will not do much for "keeping it clean"

Answer 2

Frequent partial water changes. This is very frustrating and stressful for your fish. Get a filter.

Answer 3

Well...it is very hard. You could add water plants, for a small effect. You can also buy water snails, they just go around cleaning the sides of your tank. But even those two together will have you doing frequent, partial water changes. Unless you have a lot of spare time, this can become quite a hassle.