Abstract: A filter media component containing activated carbon, which undesirably filters chlorine from water in an aquatic reservoir in which a minimum level of chlorine is desired to be maintained, is inserted into a fluid pumping path for water from the reservoir to reduce levels of cyanuric acid without purging the reservoir. Once levels of cyanuric acid drop below a target reduced concentration, chlorine and other required chemicals may be added to the water to restore proper water balance and increase the chlorine concentration to at least the minimum level of chlorine desired to be maintained. The process, which can be completed in a short period of time with sufficient quantities of activated carbon, need only be performed seasonally of periodically and avoids waste and potential damage associated with purging and replacing the water within the aquatic reservoir to reduce cyanuric acid levels.