When you mention organics, are you referring to adding nutrients which could cause other problems, such as increased phosphates and nuisance algae and cyano issues?
Not nutrients per se though garlic contains some phosphorus, iron , and organic carbon as well as trace metals including zinc which could be a concern. The allicin contains sulfur as well. These may not be an issue at low levels . However, adding an organic compound can effect many reactions and activities in a closed system . I'm personally particularly wary of any claiming anti microbial properties.