They are scavengers just sifting through the substrait looking for tiny bits of food.
If you want an algae eater you could try a plec (nice but messy fish), algae eater (does what it says on the can), apple snail or shrimp!
They will never keep your tank 100% free from algae but they will help.
My personal fav is my Amano Shrimp. They add contrast to the tank but beware... They are sensitive to some medications for fish!!
Forgot 2 say my gourami are hand feedable and it only took a week to train em!!