Raising Azolla with cow dung fertilizer like others, but it's not good. In Laos, they do the same thing. How come it's so good?
Are you adding fresh cow dung or decomposed cow dung? Very fresh cow dung can release gases or compounds that are harmful to Azolla. Another thing I would like you to check is water pH. Azolla prefers pH between 4.5 to 7.5. Please check water pH and adjust if needed.