Pond goldfish turning black

[PKS]

Hi,
I’m fairly new to pond care having inherited a ~11,000 litre pond early last year. We currently have 8 adult goldfish and around 30 of their offspring from last year. Recently two of our adult goldfish have started to turn black around the edges of the fins, tail and cheeks, and one has now started getting black scales on its back as well. I’ve read this can be due to ammonia burn but my parameters seem good on liquid testing:
Ammonia 0
Nitrite 0
Phosphate 0
KH 6
GH 7
pH 7.5-8 (somewhere in between by the colour)

Any ideas what this could be? The second fish is only black on the tail and edge of dorsal fin, but that’s how the first one started too so I’m worried it might be a global problem rather than a single sick fish.
Attached photo of ‘Goldie’ (I let my kids name them!) who was completely red last autumn.

 

[rubyduby]

That IS strange PKS...Hopefully someone on this site will be able to help to identify the cause of this..I am sorry that I have no idea...If they were young I might suggest that it could be normal color change but I am not sure since they are adults.

 

[mrsclem]

Looks like a normal color change. Goldfish and koi frequently change colors. I had a white one as well as a bronze one that are both now orange and a couple are getting the black on fins and tail. You water looks good so just keep an eye on them.

 

[Criscar]

How old are your fish? Our largest fish is 4 years old and she is still undergoing color changes (though in her case she lost her blue and the amount of black is decreasing rather than increasing). The part on the fin especially just looks like normal shubunkin fins.

 

[Criscar]

As for the speckling, do water birds ever visit your pond, or have you recently gotten some new plants that could have had aquatic snails in them? Some flukes leave black dot marks, though it’s usually smaller than that I think.

 

[j.w]

@PKS
Wonder if perhaps they don't have some Shubunkin in them as they change colors.

 

[PKS]

How old are your fish? Our largest fish is 4 years old and she is still undergoing color changes (though in her case she lost her blue and the amount of black is decreasing rather than increasing). The part on the fin especially just looks like normal shubunkin fins.

I’m not exactly sure of the age but I guess about 3 or at most 4 years old. It does seem a bit like the colour change the juveniles have been going through, but in reverse. I just never thought they went back to black again, but I am still learning!

 

[PKS]

As for the speckling, do water birds ever visit your pond, or have you recently gotten some new plants that could have had aquatic snails in them? Some flukes leave black dot marks, though it’s usually smaller than that I think.

I have recently added a new plant, but I first noticed the colour starting to change a couple of months ago, before this. The same fish developed a small self-coloured lump on its back at what seemed like the same time (but hard to be sure as I couldn’t really see them clearly when they were huddled at the bottom of the pond over the winter) but the second fish doesn’t have this. There doesn’t seem to be any change in behaviour so I guess i’ll just keep an eye on it!

 

[WaterGardener]

I think it's unusual for a fish to develop more black. It's normal to lose the black as it gets older, but the opposite would make me wonder what the problem might be.

My first thought is ammonia burn and the edges of the fins as you describe are normally the first to be burned. The black usually indicates healing so the problem may have occurred earlier and the ammonia level might be fine now. But if other fish are developing this, I would think that there is still something going on.

Are your tests current and are they the liquid type? The strips are not very accurate so they aren't too useful.

Random small black spots can be normal. If so, they are called shimmies and they develop in cold water. Once the water warms, they disappear. I have a few fish that develop those every year and it's nothing to worry about.

But, to me, the black on the fins would be a concern.

 

[PKS]

Hi @WaterGardener. Thanks for your reply. This was my general feeling as well, and the reason I’m feeling a bit uneasy about it.
My water test results are liquid and I did them yesterday, so they are up to date. We have an Oase Filtoclear 30,000 filter that’s appropriate to our pond size with goldfish, and the fish don’t seem crowded. We have several plants in the pond, the water lilies are not really doing much yet but there’s a large bog garden section with irises etc, and several submerged plants elsewhere. I haven’t been doing any water changes yet, but I have had to top up the pond a couple of times due to the recent dry weather - only a couple of inches each time. I used tap water with chlorine remover. As far as I can remember the blackening started before I added any water, and I tested the water back then and had the same results as now (I didn’t have a hardness test kit at the time but other parameters were good).
I don’t know what else to test for! All my googling hasn’t produced any suggestions other than ammonia burn, and I’m confident I’ve ruled that out!

 

[WaterGardener]

Thanks for your reply. I have no other ideas since your water seems fine. Very confusing.

There is a black spot disease caused by parasites, but I don't feel like those symptoms match what is going on with your fish.

Maybe it really is just a normal color change after all and there is nothing amiss. I hope that is the case

 

[Kimberleyc]

I have a young yellow goldfish which is also turning black down its sides but not fins. I have a liquid test system which indicates water is fine
Only one fish changing colour so I'm hoping it's a natural change, or could it be a parasite?