Self-made fish tank external filter

The simplest thing is to find a coke bottle or a green tea bottle with the right size (of course, the bigger the better).

See how you like it, horizontally or vertically. If possible, make a shadow on the outside of the bottle with plastic paper or paint.

If you put it horizontally, put it on one side of the fish tank, tighten the bottle cap, dig a hole in it, buy a dozen small pumps, connect the pipe to the water inlet, drill a few holes below to let the water out, put a biochemical ring in the bottle, and put one or two layers of filter cotton on the biochemical ring.

If the bottle is placed vertically, the bottom of the bottle comes out of the bottle mouth, and the middle is filled with filter material, and the bottle mouth is higher than the water surface. This is more suitable.

I made this for my friend. It's the cheapest.