No because they stick to the wall of their tank and clean the walls of the tank.
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They are harmless and never chase other fish. They help keep the tank clean by eating the algae. It's good to have one in any aquarium.
I suggest that you learn more about your fish in your aquarium. One of your fish might be a bottom sucker which means that they eat all of the dirt on the side or bottom of your tank. If one of your fish are bottom suckers, that's probably the reason why your aquarium is clean. If none of your fish are bottom suckers, than somebody must be secretly cleaning your tank for you.
Adding a sucking fish, like a plecostomus, can help maintain the cleanliness of the tank by eating algae and waste. However, it's not a necessary requirement for the two pet fish to live as long as you maintain the tank with regular water changes and proper filtration.
You obviously did not do your homework when it comes to the fish you have and their needs. Sucker fish do not eat poop or rubbish. (No fish does that) They are tropical fish and they are algae eaters.
There are many different aquarium animals that will clean algae off the walls of your aquarium. I will name a few: Cories, Plecostomus (AKA, Pleco) and more. There are some algae eaters that are not fish. Mystery snails, freshwater snails, and other water snails eat algae. Ghost shrimp are small and are very easy to take care of. They clean the decorations in your fish tank and eat any uneaten, leftover food.
Scoop all your fishes to another tank or tub of water and clean the fish tank just as you would normally without the fish
Depends on if you have a good filter or not, whether the water would stay clean enough. As far as getting along together, I don't think that 'sucker fish' (it is not clear what kind you mean) or angelfish would PESTER the tetras. And I certainly don't think the tetras would pester the 'sucker fish' or the angels.
Catfish do not clean tanks. That is a falacy. Sucker fish eat algae from whatever surfaces the algae grows on. Catfish are simply bottom feeders that use their feelers to help them find any food that has fallen to the bottom of the tank. Like all other fish they need fresh food. They are not specifically carrion eaters nor are they eaters of rubbish.
These fish can be taken care of just like most fish out there. Get a tank with a filter and put them in. Feed the Molly tropical flake food and the 'sucker fish' pleco algae tablets.
Your fish tank doesn't need to be cleaned. It's always clean.