If you keep tropical fish then heating the tanks will be your biggest expense. Most tropical fish come from much warmer places than the UK and usually come from large rivers or lakes so the temperature is kept quite stable. This is very important if we want to keep our fish healthy and happy. Sudden changes of temperature by even just a couple of degrees can seriously stress your fish. Stressed fish are much more likely to suffer from an illness as their immune system will be weakened. If you are... 

If your fish house is in your garage or adjacent to the house, and you have gas or oil fired central heating, then why not put in a radiator? I would not recommend running the central heating just to heat the fish house. But in the winter months you will be heating the house anyway. So the fish house will be heated for free! If you are thinking about using this method there are a couple of things to think about; - The fish house needs to be fairly close to the boiler or another radiator. - You should...