If no precipitate forms, the solution is still usable. However, you might want to check the pH in this case and adjust it to around 7.0 using either KOH or HCl as needed.
To prepare sulfur-free trace elements for hydrogen generation, the sulfate salts can be replaced with equimolar chloride salts (ZnCl2 10.0 g; CuCl2 . 2 H2O 1.00 g; FeCl2 . 4 H2O, 3.60 g). .