Fish Tank Heater

Hi all,
        After a couple of months with my small but nice fish tank I have bought a juwel 240 and have upgraded internal filter to bio flow 6 with 1000l pump. question I have is I have just started fishless cycle and wonder if the heater I have will be strong enough to cope with tank size. its a 150 w heater. will that do or should I go for higher spec. Thanks in advance. Ian

The usual requirement for heaters is 1 watt per litre. But it doesn't have to be just one heater. For a 240 litre tank, you'd need one 250W (I don't think they make 240w ones) or one 150w + one 100w. Or two 125w. A lot of people with big tanks use two on the grounds that if one stops working, the other can keep the tank warm enough until the broken one can be replaced. And if one sticks in the on position, the other will turn off and the stuck one won't be able to get the tank hot enough to boil the fish (which has been known).
If you decide on 2 heaters, leave the Juwel one in the filter and put the other at the opposite end of the tank.