Black Streaks on Guppy Tail

[Guupy42]

My male guppy has these black streaks along his tail. I could not identify them, even it I have been researching on this over the past few months. The black streaks come every once in a while, but disappear quickly, too.  I believe this is some sort of Fungal infection, as a previous fish of mine had a more serious case of this symptom (The spots/streaks multiplied over time), and died of a fungal attack suddenly a few months back. I used to add aquarium salt to treat my current fish's streaks, but recently found out that is disappears by itself after a water change. Has anyone seen anything similar on a fish?

 

5 gallon tank

Three male guppies, 1 Nerite snail

No point in describing water conditions, as it happens over time.

The first picture is of the fish that passed away. The second one is the one whos spots show up and vanish constantly. The picture was taken today before my water change.

Edited March 9 by Guupy42

[Cinnebuns]

Water conditions are still a factor in any disease. 

[Guupy42]

Okay, I just did a water change  this morning, so the ammonia level shouldn't be too high. The pH might be a little higher, because that's usually what happens after a water change. (Sorry, I don't have a testing kit) Also, the picture was taken BEFORE the water change, and the fish is back to its normal state now, so I can't be sure of the triggering water condition of this disease.

[Colu]

You can get these black streaks in the tail  with ammonia burn what your ammonia level 

[Guupy42]

That could be possible. That's probably why it usually goes away a few hours after a water change. Maybe this fish is just a little more sensetive than usual to water conditions. Thank you.

What about the other guppy (mentioned in first post), with the spots? Those would not go away, even after water changes. What could that have been? Is it still related to Ammonia Poisoning, or could it be Black Spot disease?

Edited March 9 by Guupy42

[Colu]

On 3/9/2024 at 8:18 PM, Guupy42 said:

That could be possible. That's probably why it usually goes away a few hours after a water change. Maybe this fish is just a little more sensetive than usual to water conditions. Thank you.

What about the other guppy (mentioned in first post), with the spots? Those would not go away, even after water changes. What could that have been? Is it still related to Ammonia Poisoning, or could it be Black Spot disease?

Yes it could the ammonia poisoning can cause secondary bacterial infections and damage to the slime coat what exactly are your water parameters ammonia nitrite nitrate pH KH GH temperature 

[Whitecloud09]

If you don’t have a testing kit, I suggest the API test kit, guppies can be kinda sensitive to certain water paremeters like bettas, or at least could you get a ammonia test kit @Guupy42?

[Colu]

Just noticed you put you don't have a test I would get some 5-1 test strips and ammonia tests strips or the API test kit as @Whitecloud09

[Guupy42]

Thank you for your reccomendations. I will definitely look into it sometime.

[Guupy42]

I got some testing strips, and ammonia doesn't seem to be the problem. I saw some streaks, and tested the water. The only problem was the pH was a little high, and the Nitrates were at 0.5. The ammonia read 0 ppm, so I don't think that's the problem. Could there be any other reasons for this discoloration?

Here is a picture I took right after testing the water. The streaks are very clear.

[Colu]

You could have had a spike in ammonia weeks ago  and now your ammonia gone back to zero it can takes upto 5 weeks for black marks caused by ammonia burn to go away