I am not a chemist, but I would expect that a liquid fixer would be fairly well buffered against pH changes due to normal water variations. According to Ryuji Suzuki the measurement of pH of photographic solutions is difficult with pH meter unless you have a special probe. He does actually recommend indicator papers. I wonder if your indicator papers are good for such a strong mixture of chemicals. See


FX-Universal is supposed to be slightly alkaline, no more so than much tap water. It is not supposed to be conspicuously alkaline. It is sufficiently not acidic to give the obvious benefits of alkaline fixers (especially no SO2 odour) but not so alkaline that emulsion softens noticeably.

As far as your indicator papers are concerned, I don't know why you got the reading that you did. What make/type are they?