I think what need to do is...
Take water readings, start water changes and then answer some questions.
How long between water changes? Is your tank near a window getting sunlight? Are you over feeding?
Algae is caused my excessive nutrients so you need to figure out why this is happening. Also what is your flow like?
Tell us a little about your tank, size, stock, equipment your using... Etc etc etc...
"When creating an aqua scape, strive for the beauty of imperfection, as its art and there is no wrong or right, it's left open for interpretation" James Findley