i was reading and a tip given was to use two heathers half that rated for your tank thus the two = what your tank required.

the reasons give were
1. if one broke the other would still heat the tank till you could replace it

2. if one is stuck in the "on" position the other will cut out thus no boiled fish!

while i can see the sense to this i still wonder is it worth the hassle

is anyone doing this or has it saved anyone tank?

Apart from the obvious cost differential in buying two heaters instead of one, which would be pretty negligible anyway, it seems perfectly logical to me and I'll certainly be keeping that in mind when I get around to setting up a decent sized tank.

I can't see the logic behind point 2.If heater A is stuck "on",then heater B will cut out.BUT heater A is still stuck "on",heater B couldn't possibly turn it off,so I would imagine you will still have 'boiled fish'.
But in a larger tank,then yes,2 heaters would be beneficial.Set 1 heater slightly less than the other,so if the higher 1 dies,the 2nd will kick in.
Considering the cost factor,if you have several hundreds of euro worth of fish in a tank,I would think that 30euro on a 2nd heater is a very cheap insurance policy.
Dave

I use 2x50w heaters on my marine tank. The first one is set to the max. No switching on and off causing ware and tear keeping the tank at 25-26c. The second only kicks in when the temp. drops.
My thinking is if i use low wattage heaters they wont boil the fish if they get stuck in the on position. If they both fail the ambeient temp. is around 20 in winter and up to 28 in summer.
It has worked for me so far.

I had trouble with heaters earlier in the year where the jewel one just decided to stop working. It took me a little while to notice as the tank is in the sitting room and room temp was high enough. I noticed the fish acting a bit strange and put in another heater. Amazingly this one broke aswell. Anyway the moral of the story is that I now have 2 heaters in the tank and I dont have any drop in temperature so everyone is happy. Like most things fishy I learnt the hard way.

I can see why people think it is just an added expense but as time goes on and the equipment gets older these kinds of things happen. I supose it is just a fail safe. Its like having 2 filters on the same tank. If one fails the other takes up the slack until you can rectify it.