Can't trust only one Thermometer

[smokinreefer]

If you're using a heater with those suction cup temp probes...
Please be sure the probe is SECURE.

Last thing you want is the probe to come out, giving a low temp reading and the heater to stay on and on because it thinks the water is cool.

You can end up losing alot of clams and zoas that way.
Yes I'm still bitter after a decade.

[gregzz4]

I have 5 of the Hagen floating glass therms which I use to check things. 2 read 1 degree higher than the other 3 so just split the difference. I also have a couple Big Alert Digital units and all match each time I check. I use them to calibrate my controller probes.

On a side note, I run my tank @ 78.5ish. I'd be hesitant to run a controller at your 84F. Hard on some fish and many corals. Plus depleted O2.
This will also give you more algae and cyano issues.

[Frogger]

Originally Posted by gregzz4

I have 5 of the Hagen floating glass therms which I use to check things. 2 read 1 degree higher than the other 3 so just split the difference. I also have a couple Big Alert Digital units and all match each time I check. I use them to calibrate my controller probes.

On a side note, I run my tank @ 78.5ish. I'd be hesitant to run a controller at your 84F. Hard on some fish and many corals. Plus depleted O2.
This will also give you more algae and cyano issues.

I originally set the finnex controller at 78 degrees but my water temperature was less than 74 degrees and the heater wasn't on.. I raised it to 80 and the temperature came up to about 75 to 76 before the heater turned off. I had to raise the temperature on the finnex controller so that it reads 84 before it would shut off at 78 degrees. I have been running it at this setting for the past couple of weeks and I check the temperature 2 to 3 times a day with the Vee Gee digital thermometer. It only fluctuates less than half a degree.

This means the controller is calibrated way off. So don't trust the reading on controllers.

[Cujo#31]

I refuse to run a heater without a controller to monitor the temp, and as an added redundancy my chiller is running on its own settings. That way it requires 2 system failures. As well as replacing heaters every year to make sure they are in as good condition as possible.
I also use 2 glass thermometers, one in display, one I. Sump, and I have a digital temp gauge so that I can check tank temp on controller plus 3 separate thermometers.