Temperature machinations

[Chriscz]

Ok just a little complaining about equipment. I have a 26 gal tank with a 100 W IM Helio PTC Titanium heater.
I initially set it to 78 F and. I decided to confirm the temperature with a digital thermometer and had a discrepancy between the two with the external digital thermometer reading 76. So I increased the setting on the Helio to 79 which got the digital thermometer to read 77 with an occasional 78. Everything in the tank seems happy.

But I wanted to get to the bottom of which thermometer is correct. So I brought in a third and a fourth digital thermometer to see what is really going on. Oh and there is also a thermometer on my ATO system which provides a reading as well.
Helio set at 79
Digital 1 reads 77 (occasionally flashes to 78, doesn't provide a decimal place reading)
Digital 2 reads 77.3
Digital 3 reads 79.3
ATO shows 77.2

Helio has a claimed accuracy of +/-0.1F
Digital 1 is a The Original Super-fast Thermapen 5 with a claimed accuracy of+/- 0.5F
Digital 2 is a OXO Chefpro with a claimed accuracy of +/- 0.9 F
Digital 3 is a Thermapro TP19W with a claimed accuracy of +/- 0.9F
ATO is RedSea ATO+ with a claimed accuracy of +/-0.18

The Digital 1 Thermapen 5 came with a calibration certificate, but it is the oldest thermometer of the bunch, probably 15 years old.

I have read stability is likely more important than precise accuracy (however natural coral reef settings vary by several degrees over relatively rapid timeframes with different water masses circulating through, rain and thermal mixing events. etc.)

So this is likely a calibration issue, but which one do I choose to go with? Should I err on the cooler side or warmer side?

I know this is a tempest in a teapot, since everything in the tank seems happy.........

 

[Saltyreef]

I wouldnt go down the rabbit hole of comparing non NIST thermometers.
Its a long, dark, ugly rabbit hole.

I have compared a couple different heater controllers to a current NIST calibrated & certified digital thermometer and they both were within 1 degree which is good enough for a hobby tank. (Ranco and hygger)

what you want to look out for is temp swinging more than 2 degrees on a stable day.

77 is the sweet spot but nothing wrong with 79 either.

 

[Chriscz]

Ok with three reading 77ish, I'll stick with what I have. Thanks for the reply!

 

[Mr. Mojo Rising]

My hydros as a temperature probe, so does my sump pump, the temperatures never match, and if I check with my hanna tester I get another reading. But they are all within 2 degrees of each, and the temperature remains the same on all 3 devices.

I would pick stability over trying to match the temp with different tools

 

[Largeangels]

Helios says "Resolution" 0.1, but accuracy +- 1. Cheaper like these won't be better than +- 1°F.

Just set it at 79 or 78 and leave it.

 

[MegabiteOG]

So I had the same dilemma with multiple probes in my system with different temps and whether it mattered or not, it drove me nuts. I bought this NIST certified probe and calibrated everything to it. I've used it for months now and worked out great for me. Instant reading and can check if temp is off quickly and easily.

Note that resolution is ±0.5°F which was good enough for me.

Amazon $13.08