You should do a 25% water change every two to four weeks. There is no reason to remove the fish during the water change. Make sure you stir the gravel or use a gravel cleaner during the water change. When adding water back in to the aquarium, use Tetra AquaSafe® to remove the chlorine and chloramine. Try not to change more than 50% of the water, because this will remove the beneficial bacteria and can cloud the tank.