Kori

I have 2 endlers right now in a 5 gallon tank in addition to one other sucker fish. The yellow endler seems to have sprouted a lump/tumor? overnight. I don’t have any kind of heater so my guess is the temperature is about 65-70 Fahrenheit. I have had the tank with these fish for about 7 months and have fed them the same food. I’m not sure what to do as I’m a somewhat new fish owner and could use help The tanks levels are: pH- 8 nitrate- 0 nitrite- 0 hardness- 25 ammonia- 0