Just wanted to know the main purpose for water changes... I have a 125 g mixed african tank which has been up and running for 6 months now with 20 med sized cichlids. I have only done 3 water changes since the tank has been up and running adding about 15 - 20 gallons at a time. I add about 3 to 4 gallons weekly from evaperation. Are my fish at risk?? Do I need to do more water changes?? Just looking for some thoughts