Okay well i ddi see 75 glalon aquariums, but i cna't find a heater big enough, i looked at troic heaters and they only go up to 65 glalons does this mean i need two heaters and if so, what two heaters, will the one be fine?
I have a 100 gallon tank and I have two 300 watters one on each end and it is always nice to have more watts than you need so they are not working as hard which will make them last longer.
Pooky and SoulFish make good points,
2 heaters are actually better.
One at each end to more evenly regulate temperature and if one heater were to fail the other would work well enough to keep your fish from suffering a radical temperature drop.
They have pretty good prices there and if you spend over $275 you get free shipping. I usually place orders over this whenever I need stuff. I get what I want and then buy a bunch of saltwater salt to make up the difference and not have to pay for shipping. I usually get stuff the next day when I place an order.
I've got two 100 watt heaters as well as two 50 gallon rated filters on my 55 gallon tank. One heater and one filter are also plugged into a UPS. This way I know that if the power goes out, I know my fish won't suffer soon. Also if either filter or either heater goes out, I still have one of each running to keep the tank healthy until I can replace whichever broke.
I decided on this configuration after a power outage a couple months ago wiped out an entire 10 gallon tank of mine.