Water changes are about the equivalent of changing the sheets on your bed. You wouldn't want to sleep on them after a month or so even though they may still look clean. Fish need good water conditions to prevent stress and disease, some more so than others. I'm a little confused by a syphon that sends the water back into the tank. It would seem to me that you are also putting the dirt back in the tank, negating the effort. I also don't know how it would work since a syphon works only when the outlet is lower than the intake.
As for your algae problem, do you know what type algae you have. Different fish will eat different types of algae and there are some types that no fish will eat (blue green algae). Before you buy the otos, do some research and make sure they will eat what you have. Also, try to find out what is causing the algae: over feeding, lights on too long, etc. It is better to prevent it that get something to eat it.
