The color from presoak is sensitizing dye and they should wash off in the course of normal processing. Even if some of them remain in the film after processing, it is harmless. The purple cloud is undissolved silver halides, resulting from incomplete fixing and very harmful. You should re-fix these films immediately, preferrably in fresh rapid fixer. As John mentioned, modern films especially tabular grain fulms require more vigorous fixing process. Rapid fixer with continuous agitation make it managable to complete fix in 5 minutes.(posted 8361 days ago)Overfixing (dissolving image-forming metallic silver) occurs in a fixer solution with low pH. It is negligible in weakly acidic to alkaline fixers.
If you insist in washing off the dye completely, soaking the film in water for 10 to 20 min takes care of it. Fixer remover (a simple sodium sulfite solution will do, unless water temp is high) is also an effective way to wash it off. Prolonged fixing is not the preferred way to take care of it.