Preparing for a water change but don’t have a lot of faith in the quality of your source water? Are the filters on the RO/DI unit past their prime or do you buy water from the fish store? When making water changes with poor quality source water it might be a good idea to consider running activated carbon or GFO on the mix prior to performing the water change. The idea behind a water change is to dilute the nutrients in the tank by removing “dirty” water and replacing it with much cleaner water. If the freshly mixed water is full of nitrate and phosphate, then the water change is counterproductive. So, strip those algae-fueling nutrients from the water and provide you aquarium with the cleanest possible water for the water change.