Cooling aquarium/lowering nitrates

Question
First off, I shall try to fill in all the instructions for you.
1. 80 litres
2. not too sure, but it looks big and has three chambers with activated carbon and some odd tube things... It is also suspended above the water in the tank lid.
3. had been established a few months
4. Shubunkins - 2
5. All readings fine except temp too high (not sure exactly but could tell it was too warm when I dipped my hand in) and nitrates too high.
6. All fish seem fine, swimming happily. Although one bullies the other something terrible and I am considering replacing one or both of them. One had fin rot last month, but it cleaned up an absolute treat, though had to do full water change after housemate tipped a load of M-blue in tank.

And now onto the questions!
I was wondering how I could keep my fish tank temperatures down... I leave the lights off now, as they let off a bit of heat. I also worry about the amount of oxygen, and have taken to leaving the water a bit below the filter exit so that the water disturbs the surface of the water.
In regards to the nitrate levels, I have been doing water changes to try to reduce, but my local pet shop doesn't really 'do fish' and so cannot advise me further.
Thank you for any help you can give.
Kind Regards,
Helen

Answer
Hi Helen,

You are having a host of issues because 80 litres is about 21 gallons and you need about 100 gallons or more (378 litres) to properly care for shubunkins.  These are single tailed goldfish and are really meant for ponds and not the indoor aquarium, unless, that is, you are willing to have a large tank for a couple of fish.

Goldfish need temps of 64-70 F (17-21 C) with the cooler the better.  You can buy a thermometer inexpensively at any local pet shop.  This will help you keep an eye on the temp.  Not only is the actual temp important, but the stability of it as well.  Just like you can buy heaters for tropical tanks you can also buy cooling units for aquariums to keep it down and stable.

Fish need 8-10 hours of tank light per day.  Keeping if off more than that can cause the fish to get stressed, lose coloring and you may soon see an accumulation of brown algae from lack of lighting.

You can add an airstone with airpump to the tank to agitate the water or even use a powerhead.  Hagen makes very good powerheads.

How high are your nitrates?  They should be 5-20 ppm.  Partial water changes are the only solution to this.  Depending on how bad they actually are you may need to do one 50% emergency water change with tri-weekly 25% changes and good gravel cleanings with these changes.  High nitrates indicates high phosphates which is either from overfeeding or not enough routine maintenance or too small a tank and the filtration cannot keep up.

I would either re-home the shubunkins or upgrade to a much larger tank and filtration unit and you should start to see an immediate improvement.

Good luck : ) April M.