Can't trust only one Thermometer

[Frogger]

I have always had 2 smaller heaters to protect my tank from one heater being locked in the on position from over heating my tank. This is exactly what happened, about 4 months ago the temperature in my tank started to rise and I did not notice it. One of my older hagen heaters (150watt) must of locked in the on position. It could have been earlier but I only started to notice it. I check my temperature in the tanks once a week. I noticed that the reading was 82 degrees. I keep a detailed log of my fish tank and all its parameters dating back to the day I set it up. I thought summer temperature a little higher no big deal.

It was around 4 to 5 months ago I started having problems I lost a couple fish one of them was a large yellow tang I had had for several years. (I hadn't added a fish for several years). It was eating, doing well and then one day I couldn't find it. i looked everywhere. I lost another smaller fish (pipe fish about the same time). Loosing those fish caused my nitrates and phosphates to spike for about 3 weeks. This caused my tank to crash. Followed by uncontrollable cynos everywhere. I lost about quarter of my acros and everything else looked like crap.

At the time I couldn't figure it out. It appears now that the spike in my temperature (north of 86 degrees) likely caused the problems. Higher temperature less O2 at night the largest fish by far was the first to go.

Now that I have brought my temperature down to 78 degrees everything is looking way better, my corals are colouring up and growing like nuts.

Just a side note I bought two Finnex temperature controllers (supposed to be accurate) to heat my tank and have replaced the other two older heaters. One of the Finnex's is set at 84 degrees and shuts off at 77.7 degrees and the smaller one is set at 80 degrees and shuts off at 78.1. You can't trust a single thermometer or even a heat controller. You need to have an accurate way of double/ triple checking the temperature.

I now test the temperature at least twice a day.

[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.