As others have said, otos are schooling fish and generally happiest in groups. As others have (surprisingly) not said, adding animals is not the best solution to an algae problem. I'm certainly not an expert on the issue, but the most obvious suspects are overfeeding and/or too much light. Can you describe your setup and routines? The good folks here at AC may be able to help identify the problem.
Also something to consider---while otos are great little fish, my understanding is they mostly only eat fresh algae growth. They don't eat all types of algae, and they often aren't interested in the already-established stuff.