Hi,can anyone tell me what this slime on my dads pond might be? He's had it for about 10 years with Koi carp in it and put a new pump and filter on about 4 weeks ago.You can't see very well from the photos but it's really fluorescent green.Do you think the fish might be in any danger?
Thanks
Mark
Here's a close up
Thanks
Mark
Here's a close up