I receently bought a new heater for tank, the temp was down to 71 degrees. I was kind of nervous of the temp going down any lower and loose all my fish. Iheard through verious aquarium shops the temp on african cichlids malawi and tangs is supposed to be 78 to 79 degrees. I raised the temp in an 8 hour period to 76 degrees, the guy at the aquarium where I bought 5 of my told me 'MAKE SURE YOU KEEP THE TEMP AT 78 DEGREES' , I was kind of leary of this because when I didn't have a heater my tank was always 73- 75 depending on nomal room tempature the fish looked happy they could not wait for the next feeding time. So after I got the temp to 76 then 12 am I raised the temp I barely touched the nob on the heater. I woke up at 3am the temp was now up to 79 I looked in the tank and one of my kingsizei malawi cichlids was leaning on it side WO NOT what I expected I scooped out a half gallon of water and put 75 degree water back in I didnt know what to do so I put the kingsizei in my spear tank and, after a day of laying on it's side and swimming HE made it he's alive and eating well he even established domanince again after fighting my red top hogni mouth to mouth lip locked for about ten minutes. As the temp slowly came down by it's self about 10 hours or so I noticed my Black Congo calvus laying on it's side SAD to say it died and it's my falt. SO I recamend if your going to raise or lower your temp it should only be about to 1 - 2 degees a day at the most. I also found out through the internet the tangayikan cichlid can't handle the upper temp 0f the 76-to-78 standard tank temps. I hope I helped someone, I know I sure learned alot.