its just a 5 gallon with a betta, amazon sword and some java moss attached to driftwood.What type of green algae? (spot, hair... Picture?)
Second don't get ottos for 5 gallon please
What is your routine with water changes?
What is your stock list?
How long is your light on? Timer?
If your tank was ok for 11 months what did you start adding? Tell me any change that you did make in last month-stock list, fertilization etc.