# Temperature Fluctuations



## comler (Mar 10, 2009)

I've got a 29G tank (20 tall) with a MarineLand Stealth 200W heater in it. I am running an AquaClear 50 filter. The heater is situated horizontally on the back glass, about 2" from the bottom, with the filter's pickup tube located above. 

I am using a CoralLife digital thermometer to measure the temps in the tank. The probe is located about midway up the left side glass in the front corner of the tank, so as to locate it as far away from the heater as possible to still get an average temp of the water from mid-level.

Now, I have read that CoralLife thermometers are accurate to +/- 1.5 F. I've also read that Stealth heaters are accurate to +/- 1F. The heater is set at 77F. I'm assuming that when CoralLife says their thermometers are accurate to +/1 1.5 F, they mean constantly. In other words, I wouldn't think it would be accurate to +1.5 degrees one moment, and then +.5 degrees later. 

Here's my issue: *I am experiencing fluctuations from about 76.5F to 78.2F (nearly 2 whole degrees) within a 1/2 hour time frame. I realize it is from the heater turning on and off, as I can see the heated water rising from the tube and watch the temp rise. As the heater turns off, the temp drops quickly, then slowly rises a bit (not as much as when the heat is on), finally it descends slowly until the heater kicks back on.*

Is this normal? Is this stressing the fish? What is an acceptable range of fluctuation?

BTW - I have two of those thermometers, and when I put them both in the same tank they read about .4 degrees F different. Both fluctuate as described. And, the heater and thermometer are both less than a month old.


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## woodyg3 (Mar 24, 2009)

Is your thermometer close to the heater? If so, I would move it well away from the heater for a more accurate reading.

This is a greater fluctuation than I have normally seen, but it is nothing to be too alarmed about. In nature, water temperature varies by depth, exposure to sunlight, deep currents rising to the top, etc. 



comler said:


> I've got a 29G tank (20 tall) with a MarineLand Stealth 200W heater in it. I am running an AquaClear 50 filter. The heater is situated horizontally on the back glass, about 2" from the bottom, with the filter's pickup tube located above.
> 
> I am using a CoralLife digital thermometer to measure the temps in the tank. The probe is located about midway up the left side glass in the front corner of the tank, so as to locate it as far away from the heater as possible to still get an average temp of the water from mid-level.
> 
> ...


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## ELewandowski (Mar 2, 2009)

yeah. I wouldn't be alarmed. But i would think it would keep the temp a little more stable.


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## comler (Mar 10, 2009)

The thermometer sensor is located about 1/2 way up the left side glass, in the front corner. This is about as far away from the heater as it can get, being as the heater is horizontal across the bottom of the back glass.

Before this, the heater had been vertical about 8" to the right of the filter pickup tube, all the way over in the right-rear corner - completely opposite of the location of the thermometer sensor. I was still experiencing these fluctuations in that situation. Maybe I'll try moving the sensor to the front of the tank and off the end glass. 

It's just weird, because I can go to my 20G tank and look at the thermometer and it almost never fluctuates more than a few tenths of a degree. But, there are six more inches of tank in a 29G that can make all the difference in the world as far as currents go.

Thanks to both of you for your input.


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