Your fish tank is filled with 29. 12 liters of water. These models are enough. Generally speaking, it is enough to make the hourly flow less than 3~5 times of the total volume of the fish tank.

1. There is nothing wrong with waterfall filtration itself, but its biochemical cotton is a little small, and there is not enough space for nitrifying bacteria to parasitize and reproduce. Therefore, it is generally recommended to choose an outer filter barrel for raising aquatic plants. As for reducing carbon dioxide, that's nonsense. On the contrary, CO2 in the air will be brought into the fish tank with the waterfall flow, so it is correct to increase the CO2 content in the water.

2. Choose the one with large filter box and large biochemical cotton, and the effect will be good.

3. As required in 2, the larger the area of biochemical cotton, the better.

Supplement:

I recommend this one: power: 4.2W flow: 3 18L/H size: width: 17× thickness: 12× height: 25.8cm

The increased electricity bill can be ignored, but it is the biggest, and the filtering effect is definitely better than the other two.