yes you would need algae for the otos, how long has the tank been set up?? You did say it was a planted tank, correct, which the otos will like.
Also you can't always see the algae that the otos eat all the time, so if it's a tank that's been around for a bit you should have some food in there for the otos.
Also you can't always see the algae that the otos eat all the time, so if it's a tank that's been around for a bit you should have some food in there for the otos.