Hey everyone, I wasn't sure if it was better to put this in the Pond forum or in the Freshwater Fish Disease forum. However, I figured the diseases are generally the same between pond and tank fish, so I thought this would be the best place. If I'm wrong, please let me know and I'll post this in Pond instead. Anyway, I have a question about my parents' pond. I've been doing saltwater tanks for about a year now, but my mom's been having a problem with her freshwater fish that I wanted some advice on. We have a pond, about 600 gallons and 2 feet deep. It's been set up for 13 years now, give or take a couple, and there's been no fish death in it for years upon years, aside from the odd bird getting through the netting or something. Last year I tested water quality and found that ammonia and nitrite were zero. Nitrate was around 30 ppm, but that's not so bad for freshwater fish from what I see. I can't recall the pH number exactly, but I know it was acceptable. Anyway, some - not all - of fish have these spots. I'm guessing it's some kind of fungus or parasite, perhaps allowed to thrive due to stress. The fish, however, appear happy otherwise. They eagerly eat, and as I said, there have been no deaths or other symptoms at all. They're reproducing as always and there are quite a few little baby fish in the pond now. Last year we did put in a UV sterilizer to kill off the ridiculous amounts of algae we had, and the water is pretty clear now. This scared them for a few weeks, but the spots had been present before that, and at any rate they're not scared now. Please let me know if you have any ideas. This isn't a pressing issue, but it looks unsightly. They're beautiful, large goldfish. The largest one (seen in this first picture) is at least 13 years old, and he's the last of the original fish - the others are descendants of the original batch, and there's about 40 fish in total now. That's a lot of fish, but they still seem to be okay. Thanks!