temperature problem or not?

[caterpillar5]

I currently have a 2 footer with a betta and 6 panda cories. I got an aquaclear 150 and a sponge filter running... some silk plants and im using gravel as the substrate (im really considering changing to sand but not sure what's the best way to do it). I feed the cories shrimp pellets, hikari sinking wafers and frozen bloodworms. And i do 1-2 25% water changes a week.
My water parameters are:
Ammonia = 0 ppm
Nitrite = 0ppm
Nitrate = 10ppm
What the problem is that one or two of my pandas have started to lose their colour a bit the last couple days, it's the fin on the top (it's meant to be black), it's fading to whitish greyish colour? have no idea why tho.
What the problem could be i think is that the temperature is out of control in my tank for the last couple days... it's been around 37-42 degrees celcius where i live so the tank is having a hard time keeping cool... tank temp is around 27-29 degrees... nearing 30 degrees!! i don't know what to do... i already have a fan blowing the surface of the water, and i can't freeze any water in my fridge and float bottles of frozen water because my freezer is too small and i can't put anything in it... any ideas anyone? firstly what im really after is that, what seems to be the problem with my pandas? could it be the temp? or maybe something else?
Thanks

 

[BobK]

Some fish have been known to have their colors fade when they are stressed. That's the only thing I can think of - they're stressed due to the temperature fluctuations. I've heard Panda's are much more sensitive than most cories and I lost 3 of 4 in an ich outbreak several months ago. Hope this helps. Don't know what to say about keeping the tank cool besides being away from a window or a heating/air conditioning vent. Have you tried turning on the A/C? Is it available in that room?