The phrase "not up to standards" indicates that something falls short of the acceptable level of quality expected. To express this idea more effectively, one might consider using one of the following synonyms: substandard, inferior, inadequate, or unsatisfactory. Each of these words conveys a sense of not being good enough or falling short in some significant way. Other possible synonyms include unacceptable, deficient, or unqualified. While these words may have slight nuances of meaning, they all convey a sense of something being below par and not meeting the expected level of quality. By using precise and appropriate language, you can more effectively communicate your dissatisfaction with something that is not up to standards.