It cant hurt to do a big water change.
If there is to many nutrients in the water causing the algae then a
pwc should help.
Scrape all the algae off the glass before the change. Gently Rub the algae off the plants. Let everything settle to the bottom or get filtered out of the water before starting the water change, maybe a hour or 2.
Be sure to vacuum the gravel. Push the syphon down into the gravel all the way to the bottom of the tank. Slowly pull it out of the gravel. This will deep clean it. Pull everything out and clean it before filling the tank back up. This includes the filter and heater.
Some may say this is going to far and may cause the tank to cycle. Yes this is extreme but should help slow the regrowth of the algae.
See if a
lfs can do a phosphate as well as nitrate test or buy the test kits.
Did you find a way to keep direct sunlight from hitting the tank?
Did you limit the time the tank light is on? 8 hours should be plenty. I use a timer on my tanks so I cant forget to turn them off.
If any flake food hits the bottom of the tank you are overfeeding. This is a very common new tank owner mistake. The uneaten food will break down and become food for algae and or pollute the water.
Good luck.