I use Michael Smith's Amidol formulae because shipping is getting really expensive, and the Lodima prints come out so nice. I do get a weird floating goopy-looking precipitate after the sodium thiosulfate sits for 24 hours. Tests say it's still good, but I never saw it with Kodak fix--maybe it's just the result of evaporation and the Na-thio coming back out. I'm not a chemist.