I was preparing from scratch the kodak f5 fixer omitting the acetic acid and the potassium alum since I have them both in the Tetenal hardener: sodium hypo 240g sodium sulfite 15g boric acid 7,5g water to make 1lt then I allowed the solution to warm up and added the tetenal hardener (potassium alum and acetic acid). Immediately a sludge of alluminium sulfate formed. How come? Is the f5 fixer built to avoid just this? Second question: If I use the tetenal hardener as a stop bath, will I loose the mordanting effect of potassium alum due to the following bleach bath?