Fish unwell help

[leegmac]

Hi all, I must say a big thanks for all the great advice people give on here. It really is helpful to us newbies.

I have a problem with one of my fish, it has a yellow looking blister or sore on its back and I don't know if I should be worried or not. I've tried to get a pic but it's really difficult ....I've attached my best shot...

 

[cas]

I can't really tell by the picture. Is it a blister, or is it algae growing from a wound? This spring one of my fish had a green spot on its back, which was algae. I could not catch the fish to treat it, so I left it in the pond. After a few months the algae disappeared and the wound healed on its own.

 

[leegmac]

It might be a blister