I just started to my experimenting with salt printing. I really like the process and the look of salt prints. I got a Bostick and Sullivan kit and it came with 250g of Sodium Thiosulfate which I didn't use, but the rapid fix that I already mixed up. I noticed that the rapid fix bleached the print if I fix it too long. Should I stop being lazy and mix up the Sodium Thiosulfate and use it instead of the rapid fix? Is there a difference between the two fixers?