The nutrients that the algae need are locked up in the algae. When there is no more nutrients the algae will start to die and be easy to detatch from the rocks and walls. Then you can blow it off and suck it out.
It will be an endless cycle if you keep changing water because then you are adding iodine, iron, manganese etc that is in your new water. Algae needs more than nitrates.
You have been changing loads of water, did your algae go away?
Then you can change water, the algae may again grow, but it will be less and you can do the same thing. Remember algae almost always grows in very new tanks with all new water. Think about that. It almost never grows in old, dirty systems. Think about that too.