Cactus was tested as a natural way to clean dirty water. The researchers compared it to a chemical called alum. They found that cactus can remove 74.9% of dirt from water, almost as good as alum. The best amount of cactus to use is 0.03g, while alum needs 0.2g. Cactus works best when the water is not too dirty, around 41 NTU. Alum works better with dirtier water, around 81.5 NTU. Cactus likes acidic water, while alum prefers neutral water.