HELP!!!

[cichlid savage]

After my weekly water change yesterday I woke up this morning to my 2 big cats DEAD. My planiceps about 14" and my paulicea at a hair over 12", were both belly up in the same corner of the tank. At first I blamed my demon RD, but now she is gulping air from the surface. What did i do wrong? How do I save my RD? They seemed fine when I turned off the tank light and went to sleep last night. Pix attached.

 

[freeskierrocket]

check temp.....heater malfunction????..........if not test water parama and pls post results..........sorry for the losses

 

[cichlid savage]

Temp-80
Ph- 6.6
Nitrites-0
Nitrates-10 ppm
Ammonia-.25ppm
Last waterchanges 2 days ago day before cats died 80%

If it wasnt the water it had to be the RD. As she is now chillin no gulping air or anything.