Article is focused on reoxidation processes during filtration of aluminium alloys. Many of our experiments proven, that when using filtration media in gating system, reoxidation occurs. Main goal of this article is to point out reoxidation problems occuring during filtration of aluminium alloys. Reason to conduct this works was anomalies discovered by experimental casts, witch pointed out, that after filtration of primary alloys, small oxide films was detected. Oxides was absent, when we poured without filtration media. Simulation software ProCast was used during our research.