I think needing to clean the glass once a week is typical and should be standard pratice. I use a mag float and run it across my acrylic daily. This helps beat the algae back so that when I do my weekly water changes the scrubbing I have to do ends up being alot less vigorous than it would be if I wasn't using the mag float daily. I highly suggest that you look into a magnetic cleaner. It's a very useful tool and is quick & simple to use.
Get your phoshate tested. If the algae is due to phosphate you'll know it'll be a simple matter of removing it. If it's not phosphate caused we'll come up with a different plan of attack.