First of all, talk about your misunderstanding about raising ornamental fish. It is not recommended to mix cold water fish with tropical fish. One of them must have difficulty and humble life in this fish tank. Hmm. How interesting

If you keep tropical fish, it depends on what tropical fish you keep, small ones: moonlight, black Mary, silver Mary, golden ball, silver ball, silver screen lamp, traffic light and so on. The excretion of these fish is small, so goldfish can buy a waterfall filter. Because of the small discharge, the water quality is not easy to deteriorate. It is said that active nitrifying bacteria are not needed.

If you keep goldfish, the goldfish will have a large displacement, the filtration system will be stronger, and waterfall filtration will not work, so you should use the second scheme you mentioned, three-in-one top filtration. Because of the large amount of goldfish excretion, it is necessary to clean the filter cloth frequently, and it is found that the fish collectively refuse to eat (generally novices prove that ammonia exceeds the standard). At this time, active nitrifying bacteria can be used to improve the water quality, and then part of the water can be replaced immediately.

You should know what the active nitrifying bacteria are for, and don't throw them away casually.

If you insist on polyculture (goldfish and tropical fish together). That depends on what goldfish and tropical fish you have in Yaoyang. If the goldfish is beaten by tropical fish, the life of tropical fish will be even more sad, and the big goldfish of tropical fish will also be bitten.

I can't answer your screening question because I don't advocate this kind of mixed culture.