Neon tetra keeps dying one by one

[CiderLovesFish]

pH:7
Nitrates:0
Hardness:75
Nitrite:0
Ammonia: safe
KH/Buffer:80
Water Temperature:72

My neon tetras, which were very healthy in the past, started dying out after I introduce some Endler fish. Not sure if it is due to some para brought by the Endler or if it was my water quality. The syptom seem hard to breathe and then die. 

I have changed my water and added some para guard.

Does anyone know what could be the root cause and what's the best way to rescue a weak neon tetra?

Thanks a lot!

 

[Colu]

When did you lose your first fish how long from the start of symptoms before they died have used any medication if so did you see any improvement after treatment 

[CiderLovesFish]

Thanks! Usually dies within a few hours after noticing the symptom.  Did a big water change and used para guard. Still see one or two breaths very fast compared to others.

Edited September 24, 2023 by CiderLovesFish

[Colu]

With the symptoms your seeing and how quickly they died once you see symptoms it could be a bacterial infection what I would treat with kanaplex @CiderLovesFish

[CiderLovesFish]

Thanks for the suggestion, @Colu! I just placed an order for it in case I need it.  I raised the temperature of the tank last night and looks like it's getting better. So far no more fish have died.