Pool owners add cyanuric acid pool water to bond with the free chlorine in the pool and prevent the chlorine from dissipating due to the sun's ultraviolet rays. Too much cyanuric acid in outdoor pools reduces the effectiveness of the chlorine in fighting bacteria in the water. When levels of cyanuric acid reach above 100 parts per million (ppm), the pool water is in serious trouble and the levels must come down right away.
Test the water with a test strip specifically for testing cyanuric acid levels in pool water. Stick the strip in the water, pull it out and compare the color of the strip to the color chart that comes with the kit. If the cyanuric acid is above 80ppm, you need to reduce the amount of cyanuric acid in the pool. The ideal reading is between 30 and 80 ppm but 40ppm is enough to keep the sun from destroying the amount of free chlorine in the pool water.
Rent or purchase a submersible sump pump from an equipment store or pool retail outlet store and plug in the pump to a power source.
Attach the garden hose to the submersible pump, using a connection for the hose on the left or right side of the pump, depending on the make that you are using. Run the other end of the hose away from the pool. The water from the pool will flow through the hose and out the other end.
Turn on the pump and feed it into the pool by hanging onto the garden hose. Lower the pump into the water about 3 inches. Use a brick or something heavy to hold the pump in place. Watch the pump as it works. When the water line goes down, move the pump down farther into the pool so that it is always in water when running. Drain at the pool halfway on the shallow end but do not go any more than that or you could have problems with the liner.
Turn off the pump and disconnect the garden hose when done. Hook the other end of the garden hose to the faucet. Place the other end of the hose in the pool. Turn on the water. Fill up the pool to the water line in your pool. The water line is usually visible on the skimmer plate in the pool. The water should be halfway up the skimmer plate.
Retest the water using the test strip for cyanuric acid. Your reading should be below 80 ppm.