[CheeseBoy]

So I have 5 platies in a 20 gallon tank, and they are the only fish in the tank. One started to get skinny, so I waited a few days and he was getting worse so I moved him to another tank. None of the other fish seem to be affected. I have watched the sick fish for a few days and he is getting worse. He is starting to become sluggish, but he is still eating. His poop seems to be normal and he is a little skinny. Nitrates were pretty high a couple weeks ago, like 80ppm, I got it down right away. That could be the cause of the illness. I don't know what to treat him with.

 

[Mr. Limpet]

What's the KH & pH? I learned the hard way that most livebearers don't thrive in soft, acid water.

 

[CheeseBoy]

What's the KH & pH? I learned the hard way that most livebearers don't thrive in soft, acid water.

just tested and my KH is 140-200ppm and ph is 8.2.

 

[Discusluv]

High nitrates will not kill your fish outright- but, it will cause stress which will lower immunity and open fish up to illnesses they would normally combat. Especially already genetically weak fish.
If you are only seeing one fish that is sick then it is probably a weak fish that has developed an illness from declining water quality.
Sounds like an internal bacterial infection. Aeromonas bacteria is a common bacteria in aquariums high in organic material. The wasting, weakness, could indicate this. Especially when not seeing any indications of internal parasites ( white feces and red, swollen vents in fish). If the fish is still eating it has a chance to recover, Treat with neomycin ( active ingredient in Seachem Neoplex) in food. Here are the directions: Seachem - NeoPlex

 

[CheeseBoy]

Got the Neoplex. Just started dosing. I'll see how things go.