Orandas tail has a thin black line (not ammonia)

[WagglePets]

So I inspect buttercup my oranda pretty often just because he’s precious to me and today I noticed on his tail he has a very thin black line on the fringe (very outside of it) and it looks almost like some of it disintegrated..... oh my goodness I hope it’s not fin rot I am guilty of having high nitrates but no ammonia or nitrite I did a 50% wc the other day so yeah.. I’m scared if it is fin rot how do I cure it and how did he get it and is my little fantail in danger??? I can’t get a picture cuz he moves around constantly and it’s such a small black line almost like the size of a hair (no it’s not poop lol)

ammonia 0
nitrite 0
nitrate 20-30
ph:I’m testing right now but I’m pretty sure it’s 7.6

 

[NearMeBettas]

So I inspect buttercup my oranda pretty often just because he’s precious to me and today I noticed on his tail he has a very thin black line on the fringe (very outside of it) and it looks almost like some of it disintegrated..... oh my goodness I hope it’s not fin rot I am guilty of having high nitrates but no ammonia or nitrite I did a 50% wc the other day so yeah.. I’m scared if it is fin rot how do I cure it and how did he get it and is my little fantail in danger??? I can’t get a picture cuz he moves around constantly and it’s such a small black line almost like the size of a hair (no it’s not poop lol)

ammonia 0
nitrite 0
nitrate 20-30
ph:I’m testing right now but I’m pretty sure it’s 7.6

Could you fill out the emergency template to give a little more info on him? Could you possibly get a picture of buttercups fin?

With the information given right now on his fin and no pictures, your perimeters are great (besides the little bit of nitrate. Debatable safe zone is 40ppm and under) I dont think that is the right conditions to cause fin rot as far as perimeter goes. Stress can be another factor. Anything new in his tank, temp, etc? Does he have black as a natural coloration anywere on his body? If he is under 2, in my experience goldfish tend to change color a lot in that time zone. If he is lacking black coloration everywhere else but that hair like line though id think it very unlikely that it is natural coloration.

 

[WagglePets]

Tank
What is the water volume of the tank?
How long has the tank been running?
Does it have a filter?
Does it have a heater?
What is the water temperature?
What is the entire stocking of this tank? (Please list all fish and inverts.)

Maintenance
How often do you change the water?
How much of the water do you change?
What do you use to treat your water?
Do you vacuum the substrate or just the water?

*Parameters - Very Important
Did you cycle your tank before adding fish?
What do you use to test the water?
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia:0
Nitrite:0
Nitrate:40 (even though I just did a wc)
pH:7.6

Feeding
How often do you feed your fish?once maybe twice a day
How much do you feed your fish?a little pinch
What brand of food do you feed your fish?new life spectrum
Do you feed frozen?yes brine shrimp
Do you feed freeze-dried foods?no

Illness & Symptoms
How long have you had this fish?about a year and a half
How long ago did you first notice these symptoms?last night
In a few words, can you explain the symptoms?looks like a piece of his tail has rotted away and the edges are black
Have you started any treatment for the illness?not yet
Was your fish physically ill or injured upon purchase?no
How has its behavior and appearance changed, if at all?his behaviors the same I think

Explain your emergency situation in detail.
(Please give a clear explanation of what is going on, include details from the beginning of the illness leading up to now) I’m thinking about rehoming my few inch fantail cuz of the bio load sadly anyways I noticed last night a bit of buttercups tail has like rotted away and there’s a black line on the edges but it’s not terribly bad I’m just scared it’ll get out of control
Oh sorry I forgot a part it’s a 20 gal tall and 1 big sponge filter and a big hygger filter and yes a heater it’s 70-72 degrees and I change water depending on nitrates
The entire stocking is buttercup and my fantail