Hahahaah...the OP has all the answers. Why posting here? Yeah, is the city water. What? No CO2. 10 hours of light. 200w+ T5HO light in a 75g tank. Underdosing ferts. Surely, that can't be the algae farm I am trying so far to setup.
For the OP, let's get real. Anything you have told us so far are the perfect conditions to grow algae. The city water is the least you have to worry about. If you worry so much about the city water, go use RO water.