Black patches on tetras

[Nikoletta7]

Hi,

I've been having some problems with my tetras for a while, and I just can't seem to get to the bottom of it.
I've been to two fish shops that have said my water is fine. The 2nd said the hardness was a bit off so gave us something to bring it to an acceptable level, but he also said he wasn't convinced it'd be the thing causing the problems. We've tried so many medications over the past 8 months or so, but we still seem to lose the tetras in the same way. At first I thought maybe they were old, and got tumours? But this is a second batch and they were babies when we got them and the same thing is happening again.
They start off with a black lump at the base of their tail then their front fins get the same and eventually its like it rots off, and then they die. The black phantom tetra in the picture has now died unfortunately.

Has anyone got any idea what it is and what to do?
We've had so many fish die in this tank, not just tetras of all unexplained illnesses I'm getting quite fed up and not even loving having the tank anymore .

Its a 4ft tank, had a external filter, live plants, no aggressive fish at one time we had a beta and 3 apistogrammas and that was as busy as the tank got for bigger personalities, which they actually got on ok. Were now down to one apistogramma, about 10 tetras, and corys and pleco.

Thankyou in advance.

 

[jaylach]

I think that you forgot the picture...

 

[Colin_T]

Hi and welcome to the forum

Pictures and video of the fish and tank?

What are the tank dimensions (length x width x height)?
How long has the tank been set up for?
What other fish are in the tank?

What sort of fish have the problem?
How long have you had the fish for?
How long after you get the fish does the problem start?

What is the ammonia, nitrite & nitrate of the water?
What sort of filter is on the tank?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the aquarium?
Do you have separate buckets that are used specifically for the fish tank?

What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).