This really just comes to dilution and math to be honest. Some peptides like Epitalon and Reta I do with 1mL because then it's less to inject. Others like MOTS-c I want more diluent because it stings. GHK-Cu comes in a 3mL so in our household we've always used 3mL bac water. In other words personal preference.
How much BAC water are you guys using?
I keep seeing different answers depending on who you ask. Do you normally use the same amount for every vial, or change it based on the peptide and vial size? Mostly wondering what makes the math easiest without ending up with a huge injection volume.