One of the most frequently regurgitated pieces of bad advice that we find in the hobby is people claiming that it’s the water that contains the bacteria needed to maintain the nitrogen cycle. This advice usually pops up when hobbyists are moving their tanks or gearing up for a new build. Often, the claim is that the “matured” water full of bacteria will reduce a new aquarium’s cycle time. While the water does hold some bacteria, it’s actually the aquarium’s substrate and filter material that houses a majority of the bacteria. Because of this, the water is essentially useless in every respect other than providing essential substances, like calcium and magnesium for coral growth, and diluting dissolved organics that fuel algae growth.