Depends on room temp. You may be able to do with less. A 200w may be too much, and it may be preferable to do with less. For typical room temps of 70 or so, a 200W should be enough. Going too high is much more of a risk that going too low. 'More power' is not what you want when it comes to heaters.duke105077 said:can i get away with a 200w heater in a 90 gallon?