SICK FISH

[Ryajohns]

Hey guys, I’ve I’m dealing with a odd issue and can’t figure out what is going on. I have a smaller 20 gallon setup (wife’s) this tank hold 8 tetra multi types 3 diamond 2 serpae tetras 1 black widow tetra and 2 bloodfin
The issue is I had more 1 serpae has died 1 diamond and 1 bloodfin the fish are opening their mouths very wide like they can’t breathe and I originally thought maybe oxygen so I got a air stone no help I then ran a cycle of furan-2 and thought it was going to get better and today another bloodfin has opened its mouth some parameters are
Water temp- 78°
nitrite is within safe range below .040 ppm
Nitrate is within safe range below 20 ppm
PH is around 7.5-8.0 (hard to tell with color chart)
No ammonia showing up
The only thing i have not tested is my water hardness.
I open to any recs. so I don’t have to watch these fish suffer and die

-thank you

 

[The Morning]

Need to figure out why your nitrite levels are above zero. Anything higher than zero is not good.

 

[tlindsey]

Any positive reading of Nitrite is not safe. Agree with The Morning . I don't know if the Furan is safe for beneficial bacteria. If not your aquarium will go through a cycle process again after medicine is removed.
Welcome to MFK

 

[kno4te]

Any positive reading of Nitrite is not safe. Agree with The Morning . I don't know if the Furan is safe for beneficial bacteria. If not your aquarium will go through a cycle process again after medicine is removed.
Welcome to MFK

Furan can knock out ur beneficial bacteria.

 

[Ryajohns]

Ok gonna do a few 25% water changes over a week or two and see if that helps I’ll get some of the tank start to help bacteria growth again and I’ll get a exact on the nitrite I assume 0 but the test I have just shows it’s under 20 ppm doesn’t give me a better result thank you all