Is the bottom filter (type of waterfall filter) true or false

I want to learn about waterfall filter knowledge. Two times I set new aquarium and new golden fishes then they any fungus disease to catch. I use fibers filter above water. What's true? Is the inside filter more better than waterfall filter?

They both have good points and bad points. A water fall filter does a better job of adding oxygen to the tank, but a submersible filter can usually clean out the corners better.

You are probably having your fish get sick because of a lack of beneficial bacteria. This bacterial cycle turns fish waste (ammonia) into nitrites, and then converts the nitrites into less harmful nitrates. You change part of the water weekly to keep the nitrates from reaching toxic levels. And the carbon in your filter removes many of the other toxins.

When maintaining your tank, you have to be careful not to stress the bacteria by using water with no chlorine and the same temperature as the tank. If you clean out too much of the tank, the bacteria starve to death before your fish start pooping again.

I don't feed my fish for two days after a water or filter change, so the bacteria has a chance to recuperate.

When you set up a new tank, it takes time for the bacteria to develop. Ask the pet store for a handful of gravel (keep it wet) from one of their tanks to seed your new tank. You can put it in a mesh bag (even a stocking leg) if you don't want it there permanently, but leave it in for a week. Only add one fish every four days or so, and don't feed the fish for two days after you put it in (fish can go a week without eating).