The material is fully described in the information sheets at the link given by the OP. Is there a specific reason for thinking the information is wrong?
It's the standard sodium thiosulfate + sodium metabisulfite fixer.
Metabisulfite (= disulfite, S2O52-) in hydrolized in water to give hydrogen sulfite (HSO3-), which is an acidic anion.
It's the standard sodium thiosulfate + sodium metabisulfite fixer.
Metabisulfite (= disulfite, S2O52-) in hydrolized in water to give hydrogen sulfite (HSO3-), which is an acidic anion.
Most rapid fixers today are somewhere around pH 5.5, and the most advanced ones are at pH 6.5. Therefore, for a fixer, pH 4.6 is quite acidic, especially if you consider that fixers turn more acidic over time, and that Thiosulfate disintegrates as pH goes below 4.