You're right on both accounts. They sell mostly marine fish and they supply me with RO water. I'll start using tap water and dechlorinator...see how I get on. Will be much easier to do 50% water changes then. Although I have to ask, if my nitrites, ammonia and phosphates are in safe levels, is a 50% water change per week necessary? Why do we need to change water that often, or is it keeping the water fresh?