I am looking to warm up my coldwater tank slightly (due to the cold temperatures in Scotland at this time of the year) and have purchased a Interpet 150W Delta Therm heater.

Currently, the tank temperature sits at 17 degrees celsius. The heater's lowest setting is 20 degrees celsius, however I have been advised that 22 degrees is a safe temperature for my two fish that live in the tank (one 5 year old comet and one 6 month old shubunkin).

The tank is 70ltrs, so, according to the box, the heater is the correct size for the tank capacity.

Can anyone confirm that 20-22 degrees is a safe temperature for my tank? I understand I cannot raise the temperature more than +- 2 degrees celsius at any one time.