One thing to note about those magnetic glass cleaners is that most of them are not safe for acrylic tanks and are only to be used on glass tanks (they will scratch the acrylic).
Oto's are great little work horses provided you have good water conditions. I know a few people and there are a few members on this board that have had a tough time keeping these little guys healthy, though others have had no problems at all. Aside from them though, it might be a good idea to take measures to prevent the algae from even forming to begin with. To that end, do you have live plants in your tank or do you leave your lights on all day? If you have plants, then you can break up your light cycle to 5 hours on, 2 hours off, and 5 hours on again. Algae generally needs a non-stop photosynthesis cycle to grow. If it starts on the cycle and then all of a sudden loses it's light source, it breaks it's cycle and has to start all over again and never gets a chance to thrive. If you don't have live plants, then if you have ambient light in the room (from windows or whatever) then it's ok to leave the lights off when you aren't around to enjoy them. Also speaking of windows, is the tank near a window where it's getting exposed to sunlight? If so and you can move it out of direct sunlight then that will help a lot. If you can't move it out of the locations it's in, then maybe a screen for the tank or shades for the window would go a long way to lessen the amount of algae growth. Another cause of rapid algae growth is high phosphates in your tank. Without live plants in the tank to absorb them, the algae have all they want to eat available to them. Check your food that you feed, they should have low
phosphate %'s (like less then 1% preferably). More frequent (but smaller) water changes might be in order too as
nitrate is a good source of food for algae as well. So there are a lot of things you can do to keep it from growing in the first place.