Is it warm or cold water???
Is the algae in the water or on the glass?
Do you have a filter? and an aerator?
I had a friend who had tropicals, she liked to have the tank well lit and had the tank light on for too long each day which resulted in much algae. She was forever using treatments with very little sucess until she found out she needed less light!
I only have goldfish, approx 250L, if it gets a bit glumpy on the glass I go in with a good clean cloth and simply wipe the glass, then remove some of the water and replace, give the filter a good rinse out etc.
Have you ever seen the magnetic cleaners, saves you getting your hands wet!!
its black algae and it is because i left the light on too long as i lost my timer. i have now found the timer and reset it, so i shouldnt have the algae problem once its been shifted. as its on the rocks/plants as well i really need to get the treatment sorted ASAP as its looks horrible, altho my pleco is having a good old munch