Need help "dialing in" a heater

[jarrodaden]

As posted on a different thread, my son is doing a science fair project. I need to get my tanks set as close as possible to 75 and 80 degrees respectively.

Can anyone tell me how much flunctuation I should expect?

I am using a 5 gallon covered tank with a 50W (smallest I could find) heater.

My biggest problem is that the smallest adjustment seems to result in a huge change in temperature. My problem might be that I am not giving the heater long enough to catch up and settle in.

Any input would be greatly appreciated.

[Astex]

How steady is the surrounding air temperature? Such a small volume, if the air temp varies a bunch, the tank temp is more likely to fluctuate as well.

[PhishPhreek]

Temp set point

I one tank, raise the temperature to what you want to maintain.

Add both heaters and adjust them untill the pilot light just goes out.
you can tweek it back and forth a couple of times if you want but make as small adjustments as possible. You won't be able to get any closer than that.

That is called setting the "zero" on your thermostat.
Unfortunately there typically is no adjustment for "span" on aquarium heaters so you have to live with what the manufacturer provided.

[jarrodaden]

For a typical heater, what is a typical range for the flunctuation of temperature from high to low at a given setting?

[cameracorpus]

The bigger the heater, the faster it will heat the surrounding water, and it will possibly turn off before the rest of the tank can be heated. Low water circulation makes it worse. You need a heater small enough to stay on while the water circulates. You may try to place it in the water flow, that may help if the wattage is too high for the tank.

[geoff_tropheus]

you might want to consider a reptile heater that covers the bottom of the tank for a more even heat distribution.

[PhishPhreek]

For a typical heater, what is a typical range for the flunctuation of temperature from high to low at a given setting?

usually around 2 degrees the better ones claim +/- 1degree

http://saltaquarium.about.com/od/toppicks/tp/TPheaters.htm

[jarrodaden]

So far this one appears to be within 1 degree. Unfortunately, it doesn't want to heat more than about 78.9.

I will get it sooner or later. It's a trial and error thing...