Algae is normal and expected in a tank of water and can be a sign that you have a healthy environment...with that said-it still needs to be controlled-with anything in a closed system too much can be a bad thing even when it is a good sign
First you need to ID the algae-once you know what kind it is you will know what causes it and how to control it
Green algae on the back wall is good, algae on the plant leaves can hinder plant growth and can be bad
Most common causes are too much nutrients, too much or not enough light, the wrong lights, old lights, poor plant growth....you have to balance everything......the plants have to be able to out compete the algae for nutrients...old light bulb, wrong kelvin rating, wrong photo period and the plants can't grow well enough to out compete the algae.
Too much nutrients-are you adding plant food or just leaving left over fish food or both
The number and species of plants make a difference too
The best algae eater/controller in a closed system is the hobbyist
As posted algae eating livestock only eat some species of algae and the type of algae may not be the species they eat-regardless when you add algae eating livestock they have to be supplemented with food
In a 10g open and not divided with one Betta with live plants-good algae eating livestock (beside you) are snails, shrimp and otos-if you get otos you want at least 4-they are social fish and do best in groups and you will see more natural behavior and less stress....remember a stressed fish is a sick fish and a sick fish can make every fish sick in the tank.......