First and for most-STOP using tap water. That water treatment does NOT remove phosphates (PO4)nor total dissolved solids (TDS) and there is your answer by adding tap water your feeding the algae. Also, how old are your bulbs? If you don't know, change them! Google "Green Hair Algae" you will get a better understanding of what makes it grow.
What are you using for filtration? What are you using for flow?
Keeping and maintaining a salt water tank is a lot of work. It also requires patients and time. Don't give up!! Post here first before you buy anything else, or do anything else-lol.