Algae on glass is totally normal but...
I find doing frequent regular water changes as a regular routine, often reduces algae, removing 30% of old water every 2 days usually works for me.
This can be specially effective if you you tend to over feed, as suggested above.
And overfeeding is the most common cause.
Most fish can live very healthy lives on about 1/4 of the amount of food most people regularly provide.
another "less" likely scenario below
Some water providers add phosphate to help keep lead from leaching into the drinking water, and phosphate "could" be a factor, as algae thrives on it.
Check with your local water provider to see if phosphate is part of the normal treatment process.
There are phosphate removing filtration aids available.