Do Mollies need heaters?

Question
I have just started with 2 swordtail mollies and 2 black lyretails. I have a small 20 litre tank complete with a filter, rocks and several water plants. The mollies seem to be doing fine but is a heater needed for the mollies to survive? I am not using these mollies for breeding purposes and so far they have survived 1 and 1/2 weeks without a filter.

Answer
Hey Axel,
Mollies and swordtails are tropical fish, so they need their tank to be at a temperature of 75-80 degrees farenheit (I'm not sure if you use celcius because you use litres, I don't really know conversions from farenheit to celcius. I think it might be around 24-26 degrees [???])...which means you probably need a heater unless your tank is in a really warm room. =]
I reccomend getting a thermometor as well, so you always know what temp. your tank is.

Mollies can survive with out a heater, but it is stressful on them. Also, it's risky with their health because you don't know how long they can withstand the coldness or how low it needs to be to be too low. I know 75-80 degrees makes them happy though.

One heater I do not reccomend is Elite heaters. If you never heard of them, GREAT! they are the worst heaters ever. I had one set at a little less than 80 degrees and it shot up to over 110 degrees without any one touching it. It was set like that for weeks without changing and all of a sudden just went up...the bottom sort of exploded. It killed about seventy baby fish. =[   I haven't had trouble with any other brand then this, though.

I hope this info helps you out! good luck with the new tank, feel free to ask future questions.
Best wishes, chelsey