Don't get crazy, that little bit of algae you have in there is perfectly normal and does not mean you did something wrong.
I also boubt your tap water had anything to do with it. If you live in Queens I think it is still supplied with water through the 100 year old cobblestone lined water tunnels which is great water. When the new tunnels are put into full operation I would not use the water as they will be full of silicates and everything else that leaches out of new cement.
Algae is not a disease and you can't cure it. It grows on every healthy reef in the world and if it does not grow, something is wrong.
You don't see algae on reefs because at night armies of urchins cover every inch of the rock and they scrape the areas that the tangs cleaned in the day.
I have many times dove at night to see this.
It is not nitrate or phosphate that is causing this although those substances will cause it to grow larger and faster. We all have enough of these pollutants in our tanks to grow algae but algae needs special conditions to grow and sometimes our tanks just don't provide them.
Our corals need these substances also to nourish the symbiotic algaes in their tissues.
Algae is self limiting and will only grow when it has all of it's needed elements, as soon as one element is gone, it will stop growing.
If you could manually remove it with say a tooth brush and filter out the pieces that would hasten the process.
It is only a problem if it starts to overrun the tank, what you have is natural and healthy. Probably healthier than someone's tank where no algae will grow.
If it bothers you look at this very old picture of my reef. You don't have to look too closely to see the hair algae covering anything. Now this was a problem. Want to know how I eliminated it?
I reduced feeding and let it grow. All at once, when the nutrients ran out, it died overnight and I sucked the dead algae out with a canister filter.
My reef is almost 40 years old and this has happened a few times. Always with the same result, it disappears so don't get crazy.
I know all about the dozens of algae "cures", the hermits, snails, sea hares, urchins, tangs, phosguard, and grenades.
Time and patience will eliminate it and it will leave on it's own. Just feed much less to hasten the process.
Now I am going to say something that will elicit huge negative responses.
Don't change the water until the algae disappears.
Yes I know all about changing water but it is the water you are adding that is fueling the algae. Let the algae absorb the nutrients until they are gone and it dies or you manually remove it, then change the water with RO water.
After the algae dies, don't let it rot in the water or it will return.
Good luck