I have koi fish in my pond and apparently their fins are getting damaged and there are wounds on their bodies. anyone know whats the reason? the ph is around 7 and there is no ammonia. Its not any other animals because i have a net around it. What can be the reason? dirty water? I have a 800gallon pond with 2 Tetra PRF1500s. Whats the problem
they were doing fine for a while and this just started happening recently. 2 fish died already 

