i wonder what is *too cold* ? thats a very good question, and certainly would appreciate a good version of the right answer.......

Agreed, that is a very good question.

I don't have the answer, although I've always read that tropicals 'prefer' at temp of at least 25 deg, so try to keep that in my tanks.

Although of course, there's a big difference between 'prefer' and 'can easily survive in' - I 'prefer' temps of 25 plus myself, but living in England that doesn't tend to happen too much!

couple of things

firstly heaters are on a thermostat, they will only come on if the tank temp drops, so while you can turn them down, there's no point turning them off and you do just run the risk of forgetting to put them back on.

seoncdly and most importantly, fish can easily handle temps around 30C quite happily, some people do have problems with fish in the summer, what the fish struggle with is not a higher temp, but a lack of oxygen. as the water warms up the oxygen in the water evaporates and there is then less oxygen left for the fish. to handle hot temps don't worry over the temp too much, make sure you get plenty of oxygen into the water. this is achieved easily and effectivley by adjusting the output of your filter so it breaks the waters surface and makes little waves at the top of the tank.

For once, MW is the scientific one.

In a house that is getting hotter than the outdoors, you could consider a simple fan to direct a mild stream of outdoor air at the tank.. couldn't hurt.

~~waterdrop~~

lol, you taking the mickey?!

yeah, simple solution, keep the room the tank is in cool by sticking a fan on a timer to come on in the heat of the day at lunchtime.

lol, now its MW the engineer, putting a timer on the fan

(hope the kitten is not sticking in a paw at the ON moment!)

lol, don't be mean WD, I may not be the most practical or scientifically minded, but a timer isn't beyond my capabilities!!

actually Ian said todcay he thinks sitting with engineers is rubbing off on me

It could hurt your electricity bill!

Seriously can't see a fan doing much good to be honest.

Most rivers have a lot more water in them than the average aquarium does. Due to this large volume of water, and the fact water holds temperature better than air, most natural waterways don't fluctuate very much at all during a 24 day/night cycle. Further to that most aquarium fishes come from tropical areas and the warmer climate also helps prevent temperature fluctuations.

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What temperature is too cold depends entirely on the fish species being kept. Neon tetras are subject to 16C water in their wet season in South America. Even Discus and Angelfish end up in water that gets to 18 or 20C during the monsoon floods. Some species like Bettas & Killifish that occur in small shallow pools can have daytime temps over 30C and during a sudden downpour the water temp will drop to 20C.
Most tropical aquarium fishes should be kept between 18 & 32C with the optimum range around 24-26C, slightly higher for discus.

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For eBenZo

If you live in the UK then your house will be fully insulated. As such the tank temperature would be matching the house's internal temperature. If you have a thermostat on your house heating system then turn it down.
I live in Australia where it hits 40C outside in the shade and our houses are only insulated in the roof. Yet the internal temperature rarely gets to 30C and if you keep the house closed up during the day, then you reduce the hot air getting inside and warming the place up further. Then at night you open it up to allow cooler air in.
If you live in a hot climate then you can also use an air conditioner in the room.

You could also check the aquarium heater because it could be malfunctioning.

I live in Australia as well in the far north where it's 40 degrees in the shade for four months of the year. The fish are outside (most of them) this is not my choice, my parents will not let me keep more than a few tanks in my room. I only use heaters in winter. I find that even in small fry tanks without lids (~5-10 gallons) the temperature fluctuations don't harm the fish. I use shade cloth to protect the tanks from the sun and they are always under a roof. Leaving lids off in these conditions actually helps because any breeze at all helps to cool the tank by evaporating water from the surface.

If you find that for a significant amount of the time the tank temp is over 32-35 degrees for several months of the year you could consider investing in an aquarium chiller. However they are very expensive, use a lot of electricity, are large, ungainly and carry the side effect of causing condensation on the outside glass. I really think it's not worth it personally - it's like trying to grow rainforest plants in Alaska, you'd spend your whole time out in the garden trying to keep them alive. If you're in those sort of conditions, accept that there are some species (ie white clouds) that you just aren't able to keep.

When my tank gets too hot i direct a desk fan at it, dunno if it really works but hey!

But ya UK is pretty warm atm, i havent seen my heater come on at all apart from when i change water

If only...
Unfortunately, many houses in the UK weren't designed with warm weather in mind, no shady porches or shutters, no air con, houses crammed very close together, no room for big shady trees. It doesn't help, working at home, with 2 computers and a huge laser printer going. And then there's our insane cats who will squeeze through any open upstairs window (even when the door's open downstairs).

Still, the warm weather seems to have put my zebra danios in the mood - they've definitely got just one thing on their minds this morning, and for once it's not food...!

Thanks for everything guys, a great help as usual!

Aquarium temp is back down to around 26 deg C. after the break in warm temperature...we had rain and thunder one night, then sunny spells the next morning!

I have another which I will address in a new topic.