Well, Oto's are pretty expensive and it's always a question of how long they will last. If they make it past a year you are very lucky. Snails are cheaper and can reproduce, same as shrimps as said above.
But whatever livestock you choose they are never the solution to alga problems, if the conditions favor it grows faster than it can be eaten. Diatoms are something you patiently have to wait out, it can take weeks to months but eventually, they disappear on their own not to be seen again, at least not in numbers. To speed up this process some say reducing the light will help...
One of my tanks was littered with brown filamentous diatoms for over 6 months... I never changed a thing, all I did was wait and it went away and never came back in the 6 years this tank is running now. Somehow it will deplete its own food source, logically let it do its thing then this will only be sooner. Fighting and eradicating the algae will not remove the food source. This might be waiting it out looking at a lot with minimal effort or put energy in the fight for longer looking at less.
