There are two kinds of negative Feng Shui Qi in marriage: inborn negative Qi and acquired negative Qi. Inborn negative Qi means that the birthtimes of the husband and wife don't match and the unmatched Tiangan Dizhi characters have same Yin Yang nature, that is, both are Yin or both are Yang, whatever one of the birthtimes restricts another or the two birthtimes restrict each other. Birthtime is not changeable, but man can check if the birthtimes match before man gets marry to avoid the inborn negative Qi.
Acquired evil Qi in marriage is caused by bad home Feng Shui, wrong conductions, disadvantageous social relationship, etc. These factors are changeable and controllable. Learning Feng Shui, man can effectively prevent the acquired evil Qi.
According to Feng Shui theories, fortune is inborn but can be changed through targeted working. Inborn negative evil Qi in marriage is also not decisive to a marriage. In reality, many couples with good inborn Qi have to finish their marriage because they make too much acquired evil Qi. Contrast to this, there are also many couples with bad inborn Qi getting happy and eternal marriages through creating continually good Qi to their marriages.