MSG & KG is actually pretty cheap. I bought a pound of K-Glut powder for $12 or so. I'm working out the dosing, right now 1/4 tsp every 2 days. It'll last me a year probably at this rate.
You can get cheap MSG at the Asian market btw. I don't want to dose Na so I'm not going that route.
The amount you dose glut is enough to affect daphnia (kill off or stop reproduction).... It doesn't affect fish but I know it affect more sensitive critters. There are studies that glut affect fish fry as well.
The difference between toxin and medicine is the dosage.
Glut is not a medicine btw so the comparison is not appropriate. It's straight up a bio-toxic cleaner.