From the MSDS of Kodak Flexicolor Fixer:

Weight % Components (CAS-No.)
50 - 55 Ammonium thiosulphate (7783-18-8)
40 - 45 Water (7732-18-5)
1 - 5 Sodium bisulphite (7631-90-5)
1 - 5 Sodium sulphite (7757-83-7)
0.1 - 1 Ethylenediaminetetraacetic acid tetrasodium salt (64-02-8)

So it's fine. Not alkaline, but not far on the acid side of neutral (pH: 6.1).

It's priced well, and doesn't smell as much as the more acidic "black and white" fixers.