Tri-X fogging in DiXactol

Does someone have an idea that could help me out with this ? I am doing tests with DiXactol (different films, distilled or tap water, contamination of tank etc) and tried yesterday to develop a series of Tri-X 120 films, using a new tank, new volumetric containers and deionized water (bought from a super market) to mix it with. Opted for the two bath version. I have adjusted the dev. time to 4+4 minutes (instead of 5+5) because of a higher working temperature (26 deg. celcius). The first film came out fogged and the stain was quite strong, so I decided not to pass the film through the second bath after fixing (to increase the stain). For the remaining 6 films, I followed the same procedure and had slight fogging but quite unpleasant high max. density (high contrast) and not really satisfactory shadow detail. I believe my exposure was correct (measure with a Minolta spot meter) so I am really puzzled... Normally, The development would not affect the shadow detail, but I am almost sure that usin Perceptol I would get better shadow detail (or I have made a gross mistake while exposing the films). More than that, a two bath developer should not give high max density, unless something is wrong with it (dilution, etc). Finally, it is the first time that I get this fogging with DiXactol, and I have developed APX, Pan F and Technical Pan with it with no such problems. Could the high temperature be the problem (the normal working temp. with DiXacltol is 24 degrees, and its maker claims that using it at 25 would not be a problem, you would even not have to adjust the dev. time. I have surpassed that limit by 1 degree and heavily adjusted the dev duration (by -20% !!!). I would more tend to bellieve that the Dev-Film combination could be problematic, judging by the fact that this time was the only one that the first dev. bath came out of the tank having a deep purple colour... I was surprised, thinking that it would affect the development of the next film, but the results were the same... Would this colouring of the chemical mean it was oxidised ? Why would Tri-X oxidise the developer ? I am sure there was no chemical contamination (such as the second alkali bath getting in the first). Another (paranoid) thing that came in my mind was that the deionised water contained some acid substance (put there to keep the domestic irons cleaner of salt deposits, for instance). I guess if it was the case, it would be written on the container...

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