Okay, so I bought a 20 gallon high tank. I put in the water, I added conditioner, I added tetra safe start, I gave it a week, and then I tested the levels. Ammonia is 0, Nitrite is 0, Nitrate is 20, Ph is 7.6, temp is 78.6. After seeing that the levels were fine I went to the pet store and bought two dwarf blue gouramis, named chichi and chachi. Well after two days one of them died, I figured she was already sick from the pet store. I went back and they kindly gave me another one. Now the 2nd one of the first pair I bought looks pale and is just lethargic. The new one is swimming around fine for now. I just wanna know if anyone has any idea of what could be going on with them. I appreciate any help I can get, thank you in advance.