Originally Posted by heidiho
It is sad,i hate going there seeing that,my god it is the size of a coffee cup/./I never knew they needed a heater,he has never had one....
It is possible that because he didn't have a heater his immune system slowly lowered allowing him to get a sickness. If the water conditions are not at their optimum it stresses the fish out lowering their immune system so that they eventully get sick. Most fish are very sesitive to the water conditions.
I had this happen to me in my large tank not long ago. My nitrite levels got too high (my fault for missig a water change) and it stressed my fish so badly I had an outbreak of ich. Luckly I got it treated and only lost one fish to it.