To provide a water treating filter for effectively removing odorous components produced in used water in a fish tank, particularly ammonia, by incorporating a deodorant in a porous base material of a formed body made of a porous material.

In a water treating filter for purifying water in a fish tank or the like for keeping goldfish, tropical fish and the like, a deodorant and a deodorant holding additive for at least holding this deodorant are incorporated in a porous base material of a formed body made of porous material. As this deodorant, an iron compound based deodorizing catalyst is used. The porous material is not particularly limited as far as it is porous, and for example, nonwoven fabric, woven fabric, knit fabric, paper made, metal nets, porous ceramics and the like are exemplified. The porous base material is formed into, for example, a flat platy, a cylindrical, a tubular, a lumpy filler or the like.