How to make a small fish tank filter?

The steps of making a simple small fish tank filter are as follows; 1, in the big mineral water bottle, use a knife to open a small mouth at a quarter from the bottom, which is just suitable for the bottle mouth of the small mineral water bottle. 2. Remove the bottom of the small mineral water bottle with a knife and connect the small mineral water bottle to the bottle mouth of the big mineral water bottle. 3. Insert cotton into the bottle mouth of the small mineral water bottle, cut the filtered water quality filter material into small pieces, put the filtered water quality filter material cut in the previous step into the big mineral water bottle, and insert the bottle mouth of the small mineral water bottle into the cut bottle mouth of the big mineral water bottle. Hope to help you, hope to adopt!