Fish turning black

[Ralph Parker]

Hello.
Two weeks ago, I noticed that one of my nine fish turned half black overnight, with a couple others exhibiting smaller black spots. This was the day before I went on vacation so I couldn't really do much about it then and decided to see what happened a couple weeks later. Back now and the signs have definitely not gone away; two fish are mostly black and one other has smaller black spots all over. I have read that this could be caused by either a snail-borne infection of some kind or could be caused by high ammonia. My ammonia test kit is reading ~0.25 (the kit is ~3-4 years old and i'm buying a new one this week so IDK if this number is too too reliable). I did notice that snails were somehow introduced 1-2 months ago and they certainly procreated as I found dozens of smaller snails ~4mm all along liner walls of my pond. The pond is ~900 gallons and the fish are all about 4 inches long (i think). I have included photos (sorry for the crappy phone camera quality) of all infected specimen.
Which factor most likely caused this? Is this disease harmful or fatal to the fish and the pond? Can it be reversed?
Thank you all in advance for your help.

 

[mrsclem]

How long have you had the fish? To me it looks like your fish are just changing colors. Pond fish will do that! Goldfish usually start out dark and then change to orange but its possible they are doing things backwards! I only have koi now but have had a pure orange koi go pure white in less than a week.

 

[Lisak1]

It does look more like a color change to me as well - my fish occasionally will develop a random black spot, although I've never had one turn black from tail forward like that. Usually it's the other way around as @mrsclem said. If they exhibit no other signs I'd leave it alone.

 

[j.w]

Yep unless they start croaking off I wouldn't worry about the change.

 

[Tula]

I had one of my koi go from orange and black to black and white within a few days !

 

[Ralph Parker]

Thank you all for your responses. I've only had these guys for a few months so they're, pretty young. You're probably right, I've been monitoring them this past week and there isn't any unusual behavior or death. Thanks!

 

[MajorDan]

I am wondering what you are feeding them. If it is some color enhancing food it might be why they are changing colors. I know mine started changing colors after I started them on some HIKARI Gold Pellets Pond Fish Food.