i came home today and found a dead guppy stuck to the intake of my filter. it was in a 29 gal tank with 2 other guppies 6 cherry barbs and a dwarf gourami. it has been starting to get cold in my house and the tank got down to about 70 before i realized that the heater wasnt plugged in. that was about a day ago and the temp is back to around 75. i noticed when i was removing the dead guppy that it had red spots all over its body and one of my other guppies has a red spot on its tail that wasnt there when i got them. my water conditions are 0 ammonia 0 nitrite and 20 nitrate. the first thing i did was a water change to get the nitrates down. what could the guppy have died from? was it the water temp or are the red spots a disease that i need to treat? any advice would be awsome cause i have no clue what to do.