That we use unnatural bactericides which kill both beneficial and pathogenic bacteria. The good bacteria tend to keep the bad bacteria in check. The problem is that all the bacteria are killed and the pathogenic bacteria repopulate much faster than beneficial bacteria leading to imbalance. As noted by Bio Logic Systems Analyst Richard Gerber read more here Nutrient .me  there is a natural bactericide that is created with water, salt and electric the same used by the human body and it leaves no residue.