I lay no claim to real expertise, just a lot of research and experience. Unfortunately, that thread, while useful for dumping a lot of adulterants like MSM, inositol, MgSO4, etc, generally won't help you with n-isopropylbenzylamine, which is likely putting you to sleep and is good at causing headaches to boot. Its new grand life as not just a cut but an outright fake for meth has accelerated since 2013 when that thread ended. All those procedures are useful if a bit complex, I use them, acetone washes are easy to learn.
Getting rid of that hateful n-iso, or ISO, or IBA or the less used other (alkyl)benzamines gets super tricky. I haven't pulled it off. You have to get super specific with temperature changes and/or go for freebasing and recrystallization. Good luck! At least for me, the sleep is restorative.